Impaired bacteriologic response to oral cephalosporins in acute otitis media caused by pneumococci with intermediate resistance to penicillin

A systematic review and meta-analysis of antimicrobial resistance in paediatric acute otitis media

OBJECTIVE OF REVIEW

Acute otitis media (AOM) is the largest cause of antimicrobial prescriptions amongst children in developed countries. Excessive and inappropriate prescribing is known to drive antimicrobial resistance, but less is known of antimicrobial resistance in AOM-associated bacteria.

TYPE OF REVIEW & SEARCH STRATEGY

We conducted a systematic review and meta-analysis of bacterial prevalence and antimicrobial resistance in studies of paediatric AOM identified from Ovid Medline, Embase and the Cochrane library.

RESULTS

From 48 unique studies, 15,871 samples were included. Only 0.67 (CI 0.63-0.71) of all ear samples grew a bacterial pathogen. The most common bacterial causes of AOM in children were Streptococcus pneumoniae 0.30 (CI 0.27-0.32), Haemophilus influenza 0.23 (CI 0.20-0.26), and Moraxella catarrhalis 0.05 (CI 0.04-0.06). Resistance patterns varied amongst organisms and antimicrobial agents. The pooled proportion of bacterial culture-positive episodes of AOM that could be effectively treated with amoxicillin was 0.85 (CI 0.76-0.94), erythromycin was 0.64 (0.48-0.78) and amoxicillin-clavulanate was 0.95 (CI 0.85-0.98).

CONCLUSION

We have demonstrated the bacteriology and antimicrobial resistance patterns of AOM. Of samples which grew bacteria, on average approximately 15% of isolates demonstrated resistance to amoxicillin; a typical first-line agent. Greater understanding of local bacteriology and resistance patterns is needed to enable improved antimicrobial stewardship.

An evolutionary model to predict the frequency of antibiotic resistance under seasonal antibiotic use, and an application to Streptococcus pneumoniae

The frequency of resistance to antibiotics in Streptococcus pneumoniae has been stable over recent decades. For example, penicillin non-susceptibility in Europe has fluctuated between 12% and 16% without any major time trend. In spite of long-term stability, resistance fluctuates over short time scales, presumably in part due to seasonal fluctuations in antibiotic prescriptions. Here, we develop a model that describes the evolution of antibiotic resistance under selection by multiple antibiotics prescribed at seasonally changing rates. This model was inspired by, and fitted to, published data on monthly antibiotics prescriptions and frequency of resistance in two communities in Israel over 5 years. Seasonal fluctuations in antibiotic usage translate into small fluctuations of the frequency of resistance around the average value. We describe these dynamics using a perturbation approach that encapsulates all ecological and evolutionary forces into a generic model, whose parameters quantify a force stabilizing the frequency of resistance around the equilibrium and the sensitivity of the population to antibiotic selection. Fitting the model to the data revealed a strong stabilizing force, typically two to five times stronger than direct selection due to antibiotics. The strong stabilizing force explains that resistance fluctuates in phase with usage, as antibiotic selection alone would result in resistance fluctuating behind usage with a lag of three months when antibiotic use is seasonal. While most antibiotics selected for increased resistance, intriguingly, cephalosporins selected for decreased resistance to penicillins and macrolides, an effect consistent in the two communities. One extra monthly prescription of cephalosporins per 1000 children decreased the frequency of penicillin-resistant strains by 1.7%. This model emerges under minimal assumptions, quantifies the forces acting on resistance and explains up to 43% of the temporal variation in resistance.

Implications of Antibiotic Resistance for Patients' Recovery From Common Infections in the Community: A Systematic Review and Meta-analysis

BACKGROUND

Antibiotic use is the main driver for carriage of antibiotic-resistant bacteria. The perception exists that failure of antibiotic treatment due to antibiotic resistance has little clinical impact in the community.

METHODS

We searched MEDLINE, EMBASE, PubMed, Cochrane Central Register of Controlled Trials, and Web of Science from inception to 15 April 2016 without language restriction. We included studies conducted in community settings that reported patient-level data on laboratory-confirmed infections (respiratory tract, urinary tract, skin or soft tissue), antibiotic resistance, and clinical outcomes. Our primary outcome was clinical response failure. Secondary outcomes were reconsultation, further antibiotic prescriptions, symptom duration, and symptom severity. Where possible, we calculated odds ratios with 95% confidence intervals by performing meta-analysis using random effects models.

RESULTS

We included 26 studies (5659 participants). Clinical response failure was significantly more likely in participants with antibiotic-resistant Escherichia coli urinary tract infections (odds ratio [OR] = 4.19; 95% confidence interval [CI] = 3.27-5.37; n = 2432 participants), Streptococcus pneumoniae otitis media (OR = 2.51; 95% CI = 1.29-4.88; n = 921 participants), and S. pneumoniae community-acquired pneumonia (OR = 2.15; 95% CI = 1.32-3.51; n = 916 participants). Clinical heterogeneity precluded primary outcome meta-analysis for Staphylococcus aureus skin or soft-tissue infections.

CONCLUSIONS

Antibiotic resistance significantly impacts on patients' illness burden in the community. Patients with laboratory-confirmed antibiotic-resistant urinary and respiratory-tract infections are more likely to experience delays in clinical recovery after treatment with antibiotics. A better grasp of the risk of antibiotic resistance on outcomes that matter to patients should inform more meaningful discussions between healthcare professionals and patients about antibiotic treatment for common infections.

The importance of being specific--a meta-analysis evaluating the effect of antibiotics in acute otitis media

BACKGROUND

Whether acute otitis media (AOM) should be the cause for antibiotic treatment has been a matter of debate during the last decades. Treatment guidelines are based on less than twenty trials that have found the effect of antibiotics on symptomatic outcomes in AOM, such as pain, to be very modest. Two recent trials found a more substantial effect of antibiotics when they looked at treatment failure as the outcome. That the effect varies with the chosen outcome may not only be because the true effect is different but also because different outcomes are more or less specific for the disease in question.

OBJECTIVE

The purpose of this study was to perform a meta-analysis to calculate a composite risk ratio for treatment failure in AOM and also to investigate whether the specificity of treatment failure as an outcome differs from that of symptomatic outcomes, such as pain.

METHODS

Trials evaluating the effect of antibiotics in AOM and reporting the number of treatment failures were identified and a fixed-effects meta-analysis was performed. In addition, the literature was searched for articles providing direct or indirect figures on the specificity of different outcomes in AOM trials. A hypothetical study was designed to show how differences in sensitivity/specificity of inclusion/outcome criteria affect the results of a trial.

RESULTS

The meta-analysis yielded a composite risk ratio of 0.4 (95% CI 0.35-0.48), p<0.001 for the effect of antibiotics on treatment failure. Based on data from the literature, the specificity of treatment failure was estimated to 92-100%. The hypothetical study showed how a non-specific outcome biases the effect estimate towards the null, whereas other kinds of misclassification only decrease precision.

CONCLUSION

Future trials should focus on improving diagnostic criteria to increase precision but primarily, they should focus on choosing a specific outcome in order not to get a biased effect estimate.

Otitis media with effusion in Lebanese children: prevalence and pathogen susceptibility

OBJECTIVE

To determine the prevalence and resistance profile of bacterial pathogens present in the middle ear of children with otitis media with effusion, and to report beta-lactamase-negative, ampicillin-resistant bacteria for the first time in Lebanese children.

METHOD

We included 62 patients younger than 12 year (107 ears), who underwent myringotomy with tympanostomy tube placement for persistent otitis media with effusion. Bacteria were identified by Gram staining and biochemical tests, and antibiotic sensitivities tested by the disc diffusion method and via minimum inhibitory concentration (E-test).

RESULTS

The commonest pathogen was Haemophilus influenzae (62 per cent), followed by Streptococcus pneumoniae (26 per cent). The H influenzae resistance profile was highest for amoxicillin (81.0 per cent) and lowest for cefotaxime (19.0 per cent). There was a high risk of developing H influenzae antibiotic resistance among children with a history of smoking exposure (p = 0.001), recurrent upper respiratory tract infection (p = 0.001) or previous antibiotic treatment (p = 0.005). Fifty-two per cent of H influenzae colonies were found to be beta-lactamase-negative and ampicillin-resistant.

CONCLUSION

In these children with persistent otitis media with effusion, H influenzae was the most prevalent bacteria. It showed a high incidence of resistance to the antibiotics most commonly prescribed to treat acute otitis media.

Management of acute otitis media after publication of the 2004 AAP and AAFP clinical practice guideline

OBJECTIVES

Observation without initial antibiotic therapy was accepted as an option for acute otitis media (AOM) management in the 2004 American Academy of Pediatrics and American Academy of Family Physicians clinical practice guideline. The guideline also recommended amoxicillin as the first-line treatment for most children, and analgesic treatment to reduce pain if it was present. Our objective was to compare the management of AOM after publication of the 2004 guideline.

PATIENTS AND METHODS

We analyzed the National Ambulatory Medical Care Survey, 2002-2006 (N = 1114), which occurred in US physicians' offices. The patients were children aged 6 months to 12 years who were diagnosed with AOM. The time comparisons were the 30-month periods before and after the guideline. The main outcome was the encounter rate at which no antibiotic-prescribing was reported. Secondary outcomes were the identification of factors associated with encounters at which no antibiotic-prescribing was reported and antibiotic- and analgesic-prescribing rates.

RESULTS

The rate of AOM encounters at which no antibiotic-prescribing was reported did not change after guideline publication (11%-16%; P = .103). Independent predictors of an encounter at which no antibiotic-prescribing was reported were the absence of ear pain, absence of reported fever, and receipt of an analgesic prescription. After guideline publication, the rate of amoxicillin-prescribing increased (40%-49%; P = .039), the rate of amoxicillin/clavulanate-prescribing decreased (23%-16%; P = .043), the rate of cefdinir-prescribing increased (7%-14%; P = .004), and the rate of analgesic-prescribing increased (14%-24%; P = .038).

CONCLUSIONS

Although management of AOM without antibiotics has not increased after the publication of the 2004 American Academy of Pediatrics and American Academy of Family Physicians clinical practice guideline, children who did not receive antibiotics were more likely to have mild infections. In accordance with the guideline, the prescribing of amoxicillin and analgesics has increased. Contrary to the guideline, the prescribing of amoxicillin/clavulanate has decreased, whereas the prescribing of cefdinir has increased.

Clinical outcome in children with culture-negative acute otitis media

BACKGROUND

Culture-negative AOM is often milder and associated with lower local/systemic inflammatory responses than culture-positive AOM.

STUDY OBJECTIVES

To compare the clinical outcome of culture-negative AOM with that of culture-positive AOM children.

PATIENTS AND METHODS

Children aged 3 to 35 months with AOM were enrolled in 11 double-tympanocentesis antibiotic efficacy studies documenting both bacteriologic (days 4-6 of treatment) and clinical outcome (days 11-14, end of treatment). Univariate analysis (age, gender, ethnicity, previous AOM history, and antibiotic treatment) between culture-negative and culture-positive AOM patients was performed by Student t test, ANOVA, or chi2 test. Those found to be significant were further submitted to multivariable regression analysis.

RESULTS

A total of 1088 patients (mean age, 11.95 +/- 5.96 months, 209 culture-negative and 879 culture-positive AOM) were enrolled. No differences were recorded between culture-negative AOM and culture-positive AOM patients in age, gender, ethnicity and number of previous episodes. Seventy-four percent (650/879) culture-positive AOM patients achieved bacteriologic eradication within 3 to 5 days. Successful outcome (cured + improved) was recorded in 90% (189/209) culture-negative AOM patients versus 86% (758/879) in culture-positive AOM (P = 0.086). Successful clinical outcome was more frequent in culture-negative than in culture-positive AOM without bacteriologic eradication (90% vs. 67% [154/229], P < 0.001). No difference in successful clinical outcome was found between culture-negative versus culture-positive AOM patients with bacterial eradication (90% vs. 93% [604/650], P = 0.24). Overall, the inclusion of culture-negative AOM patients in the evaluation of clinical failures rates in study patients decreased the total clinical failure rate by 9%. We present a hypothetical antibiotic efficacy study enrolling 300 patients in whom 2 drugs with different bacteriologic efficacy rates (A-90% and B-60%) were used. When the culture-negative cases (5% clinical failure) enrolled increased from 50/300 (16.7%) to 150/300 (50%), the overall clinical failure rate decreased by 36% (from 17.4% to 11.2%, P = 0.08) for the less efficacious drug, while remaining unmodified for the more efficacious drug (9.6% and 8.8%, respectively).

CONCLUSIONS

(1) Clinical outcome in culture-negative AOM was similar to that of culture-positive AOM with bacteriologic eradication and both were superior to that of culture-positive AOM without eradication; (2) Inclusion of culture-negative AOM patients in series aiming at antibiotic efficacy may falsely improve the clinical outcome for antibiotics with reduced ability to eradicate AOM pathogens.

Trends in broad-spectrum antibiotic prescribing for children with acute otitis media in the United States, 1998-2004

BACKGROUND

Overuse of broad-spectrum antibiotics is associated with antibiotic resistance. Acute otitis media (AOM) is responsible for a large proportion of antibiotics prescribed for US children. Rates of broad-spectrum antibiotic prescribing for AOM are unknown.

METHODS

Analysis of the National Ambulatory Medical Care Survey and National Hospital Ambulatory Medical Care Survey, 1998 to 2004 (N = 6,878). Setting is office-based physicians, hospital outpatient departments, and emergency departments. Patients are children aged 12 years and younger prescribed antibiotics for acute otitis media. Main outcome measure is percentage of broad-spectrum antibiotics, defined as amoxicillin/clavulanate, macrolides, cephalosporins and quinolones.

RESULTS

Broad-spectrum prescribing for acute otitis media increased from 34% of visits in 1998 to 45% of visits in 2004 (P < .001 for trend). The trend was primarily attributable to an increase in prescribing of amoxicillin/clavulanate (8% to 15%; P < .001 for trend) and macrolides (9% to 15%; P < .001 for trend). Prescribing remained stable for amoxicillin and cephalosporins while decreasing for narrow-spectrum agents (12% to 3%; P < .001 for trend) over the study period. Independent predictors of broad-spectrum antibiotic prescribing were ear pain, non-white race, public and other insurance (compared to private), hospital outpatient department setting, emergency department setting, and West region (compared to South and Midwest regions), each of which was associated with lower rates of broad-spectrum prescribing. Age and fever were not associated with prescribing choice.

CONCLUSION

Prescribing of broad-spectrum antibiotics for acute otitis media has steadily increased from 1998 to 2004. Associations with non-clinical factors suggest potential for improvement in prescribing practice.

Rates of tympanic membrane closure in double-tympanocentesis studies

BACKGROUND

Data on the outcome of tympanic membrane (TM) closure after tympanocentesis in acute otitis media (AOM) patients is limited.

OBJECTIVES

To analyze the dynamics of TM perforation closure after 1 or 2 tympanocentesis procedures performed at diagnosis and during AOM treatment.

PATIENTS AND METHODS

Study population included 113 children enrolled in 4 double-tympanocentesis studies. Only the files of patients whose first and second examination were performed by the same 2 otorhinolaryngologists were analyzed. Middle ear fluid (MEF) was cultured on day 1 and days 4-6, the latter only in initially culture-positive patients. Patients were also examined on days 11-14 and followed until days 22-28.

RESULTS

Ninety-three (82%) patients underwent tympanocentesis on days 4-6; 103 (91%) and 95 (84%) were evaluable on days 11-14 and 22-28, respectively. One hundred seventy-three ears underwent tympanocentesis on day 1 and 139 on days 4-6. Ninety-seven (86%) patients had positive MEF cultures. One hundred fifty-three (88%) tympanocentesis procedures performed at enrollment were closed on days 4-6. No differences were recorded in the closure rates as function of patient age, previous AOM history, MEF culture positivity, pathogens isolated at enrollment, and pathogen eradication on days 4-6. The 20 eardrums still open on days 4-6 were closed on days 11-14. Eleven (9%) of the evaluable ears tapped on days 4-6 were not closed on days 11-14 and 9 of 10 were closed on days 22-28.

CONCLUSIONS

TM perforation closed in most cases within a few days regardless of patient and disease characteristics, and 2 consecutive tympanocentesis procedures performed at short-time intervals are associated with good TM closure rates.

Comparison of study designs for acute otitis media trials

BACKGROUND

A framework for evaluating the efficacy of antibiotics in development as well as those currently approved for acute otitis media (AOM) is needed.

OBJECTIVE

Review strengths and limitations of various antibiotic trial designs and their outcome measures.

METHODS

A review of 157 published trials involving 36,710 subjects for the treatment of AOM.

RESULTS

AOM trials have three designs: (1) clinical, clinical diagnosis and assessment of outcomes; (2) single tympanocentesis, microbiologic diagnosis (by middle ear fluid culture) and clinical assessment of outcomes; and (3) double tympanocentesis, microbiologic diagnosis and microbiologic outcome assessment. Identifiable strengths and limitations of each design are reviewed. Case definitions for entry of children in trials of AOM vary widely. The lack of stringent diagnostic criteria in a clinical design allows for inclusion of a significant proportion of children with a non-bacterial etiology (i.e., viral AOM or otitis media with effusion). Tympanocentesis increases diagnostic accuracy at study entry; however, the procedure is confounding because of its potentially therapeutic benefit and the procedure is not performed in a uniform manner. A second tympanocentesis allows a high sensitivity to detect microbiologic eradication, but it does not correlate with clinical outcomes in half of the cases. The timing of outcome assessment also varies widely among trials.

CONCLUSIONS

Improved clinical diagnosis criteria for AOM are needed to enhance specificity; emphasis on a bulging tympanic membrane has the best evidence base. Tympanocentesis within study designs has merits. At study entry it assures diagnostic accuracy but may alter outcomes and it is useful to document microbiologic outcomes but lacks specificity for clinical outcomes. For all designs, test of cure assessment 2-7 days after completion of therapy seems most appropriate.

Persistence of pathogens despite clinical improvement in antibiotic-treated acute otitis media is associated with clinical and bacteriologic relapse

BACKGROUND

Pathogen eradication in patients with acute otitis media (AOM) is associated with a reduced risk of clinical failures, but most children in whom middle ear fluid (MEF) culture remains positive show clinical improvement or clinical cure. We investigated the relationship between MEF culture-positivity during treatment in patients with clinical improvement/cure, and the occurrence of subsequent AOM.

METHODS

A total of 673 patients with culture-positive MEF were enrolled in double-tympanocentesis studies and followed for 3 weeks after completion of treatment.

RESULTS

On day 4-6, 189/673 (28%) patients had culture-positive MEFs. Patients with clinical improvement/cure on day 11-14 (end of treatment) despite having culture-positive MEF on day 4-6 more often had recurrent AOM episodes (53/151, 35%) than those with culture-negative MEF (114/476, 24%; P = 0.007). 41/53 (77%) culture-positive patients with clinical improvement/cure on day 11-14 underwent tympanocentesis when AOM recurred and 29/41 (71%) were culture-positive. Pulsed field gel electrophoresis identity between pathogens at recurrence and those persisting on day 4-6 was found in 19/29 (66%) compared with 31/86 (36%) of the evaluable patients with recurrence and culture-negative MEF on day 4-6 (P = 0.005).

CONCLUSIONS

(1) Failure to eradicate MEF pathogens during antibiotic treatment is associated with clinical recurrences, even in patients showing clinical improvement/cure at end of treatment; (2) these recurrences are mostly caused by pathogens initially present in MEF and persisting during treatment.

Failure to achieve early bacterial eradication increases clinical failure rate in acute otitis media in young children

BACKGROUND

The objective of this study was to determine the association between early bacteriologic failure and clinical failure in acute otitis media (AOM).

METHODS

Children with AOM aged 3-35 months enrolled in studies documenting both bacteriologic outcomes by tympanocentesis on day 4-6 and clinical outcomes on day 11-16 (immediate posttreatment visit) constituted our study group. Bacteriologic outcomes were studied for children with AOM caused by Streptococcus pneumoniae, nontypeable Haemophilus influenzae or both. The relative risk (RR) for clinical failure of children with bacteriologic failure compared with children with bacteriologic eradication was the main outcome measure.

RESULTS

Nine hundred seven episodes were analyzed. Clinical failure occurred in 7.3% of 660 patients with bacterial eradication versus 32.8% of 247 patients with bacteriologic failures. The overall RR (95% confidence interval) for clinical failure was 4.41 (95% CI: 3.19-6.11), with little variation between pathogens. After correction for age, gender, ethnic origin, previous otitis history, and previous antibiotic treatment, the rate was 6.52 (95% CI: 4.26-9.99). Across clinical studies with 8 antibiotic drug regimens for AOM, the rate of clinical failure correlated with bacteriologic failure (r = 0.8967; P = 0.003).

CONCLUSIONS

In young children with culture-positive AOM, failure to eradicate the pathogen from middle ear fluid within the first few days of treatment leads to a significant risk for clinical failure.

Is bilateral acute otitis media clinically different than unilateral acute otitis media?

BACKGROUND

Information regarding the specific characteristics of bilateral acute otitis media (BAOM) versus unilateral acute otitis media (UAOM) is lacking.

OBJECTIVES

To compare the epidemiologic, microbiologic, and clinical characteristics of BAOM with UAOM in children.

PATIENTS AND METHODS

1026 children aged 3-36 months (61%, <1 year of age) with AOM were enrolled during 1995-2003. All patients had tympanocentesis and middle ear fluid (MEF) culture at enrollment. Clinical status was determined by a clinical/otologic score evaluating severity (0 = absent to 3 = severe, maximal score 12) of patient's fever and irritability and tympanic membrane redness and bulging. Multivariate logistic regression models were used to estimate the risk of BAOM and UAOM presenting with a high severity score (> or =8).

RESULTS

Six-hundred twenty-three (61%) patients had BAOM. Positive MEF cultures were recorded in 786 (77%) patients. More patients with BAOM had positive MEF cultures than patients with UAOM (517 of 623, 83% versus 269 of 403, 67%; P < 0.01). Nontypable Haemophilus influenzae was more common in BAOM than in UAOM (390 of 623, 63% versus 170 of 430, 42%; P < 0.01). Overall, the clinical/otologic score showed higher severity in culture-positive than in culture-negative patients (8.2 +/- 2.0 versus 7.7 +/- 2.2; P < 0.001) and in BAOM than in UAOM (8.3 +/- 2.1 versus 7.8 +/- 2.1; P = 0.001). Clinical/otologic score of > or =8 was more frequent in BAOM than in UAOM patients (371, 61.8% versus 200, 51.3%; P = 0.001). The estimated risk for BAOM patients (compared with UAOM patients) to present with a score > or =8 was 1.5. The association between BAOM and clinical/otologic score > or = 8 was maintained after adjustment for age, previous AOM history, and culture results at enrollment.

CONCLUSIONS

(1) BAOM is frequent; (2) Nontypable H. influenzae is more frequently involved in the etiology of BAOM than of UAOM; (3) The clinical picture of BAOM is frequently more severe than that of UAOM, but overlap of clinical symptoms is common.

Consistency of diagnostic criteria for acute otitis media: a review of the recent literature

Clinicians use various criteria to diagnose acute otitis media (AOM). Using American Academy of Pediatrics (AAP) guidelines, we reviewed the consistency of AOM diagnosis in clinical trials (1994-2005). Eighty-one percent of the studies required at least one of the three AAP criteria. Only 20% of the 88 studies met all three AAP criteria for a diagnosis. We found no association between the number of criteria met and study quality or industry sponsorship. Better agreement on the definition of AOM using AAP criteria could facilitate a more accurate clinical diagnosis and provide standardization of research and patient care practices.

Pneumococcal nasopharyngeal carriage and patterns of penicillin resistance in young children in Fiji

BACKGROUND

Little is known about nasopharyngeal carriage and the patterns of antibiotic resistance of pneumococci in Pacific nations. We set out to document pneumococcal nasopharyngeal carriage and associated risk factors, antimicrobial resistance and serotypes in healthy children in Fiji.

METHODS

A cross-sectional survey of healthy children aged 3-13 months was conducted. Nasopharyngeal (NP) swabs were collected from each child and processed according to standard methods. Antimicrobial resistance was determined by disk diffusion and confirmed by E-testing. Serotyping was performed by the Quellung reaction.

RESULTS

Of 440 consecutive NP swabs taken, 195 were S. pneumoniae-positive (carriage rate 44.3%). Higher rates were found in the indigenous Fijian population. Penicillin non-susceptibility was found in 11.4% of isolates, with one isolate demonstrating high-level resistance. Cotrimoxazole resistance was common (20.3%) and no isolates were chloramphenicol-resistant. Multi-drug resistance was uncommon. The commonest serotypes were 6A (13.2%), 23F (8.3%), 19F (7.4%) and 6B (6.2%). Thirty per cent were included in the 7-valent pneumococcal conjugate vaccine (PCV), 54.3% if cross-reacting strains were included. Being indigenous Fijian or having symptoms of acute respiratory infection were independent risk factors for carriage.

CONCLUSIONS

Pneumococcal NP carriage is common in Fijian children. Penicillin resistance has been documented for the first time in Fiji and, as a result, first-line treatment for meningitis has been altered. Being indigenous Fijian is a risk factor for disease, although the reasons for this are unclear. A low proportion of carriage serotypes are covered by the existing 7-valent PCV.

[Blood and respiratory diffusion of antibiotics. A critical analysis of predictive parameters for clinical effectiveness]

The implementation of a treatment for lower respiratory tract infections must integrate a pharmacokinetic/pharmacodynamic (PK-PD) approach of antibiotic dosing. The activity of beta-lactam antibiotics is best predicted by the duration of time during which serum concentrations exceed the MIC (T>MIC). T>MIC of 30-40% is sufficient to achieve clinical cure in immunocompetent patients. This threshold is achieved with amoxicillin for penicillin susceptible or resistant Sreptococcus pneumoniae and with amoxicillin-clavulanate and ceftriaxone for S. pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. For macrolides, the activity is best predicted by T>MIC and for azithromycin and telithromycin by area-under-the-curve/MIC (AUC/MIC). Sufficient PK-PD values are only achieved for macrolides against susceptible strains of S. pneumoniae and against M. catarrhalis; for telithromycin, an AUC/MIC>25, which is necessary for bacterial eradication, is achieved in>99% of patients for S. pneumoniae and M. catarrhalis and>90% of patients for H. influenzae. For fluoroquinolones, both peak/MIC and AUC/MIC are predictors of clinical and bacteriological efficacy. AUC/MIC required ratios vary according to pathogens and severity of diseases from 48 to 125. These thresholds are reached for respiratory pathogens; for S. pneumoniae, AUC/MIC90 ratios of levofloxacin and moxifloxacin are 96 and 192, respectively; the presence of a mutation in parC increases the risk for the acquisition of additional mutations and failure.

Empiric first-line antibiotic treatment of acute otitis in the era of the heptavalent pneumococcal conjugate vaccine

OBJECTIVES

Our goal was to estimate the local prevalence of Streptococcus pneumoniae nonsusceptible to penicillin and amoxicillin after widespread use of the heptavalent pneumococcal vaccine and to revise community-specific recommendations for first-line antibiotic treatment of acute otitis media.

METHODS

We conducted serial prevalence surveys between 2000 and 2004 in the offices of community pediatricians in St Louis, Missouri. Study participants were children <7 years of age with acute upper respiratory infections. Children treated with an antibiotic in the past 4 weeks were excluded. S pneumoniae was isolated from nasopharyngeal swabs using standard techniques. Isolates with a penicillin minimum inhibitory concentration >2 microg/mL were considered to be S pneumoniae nonsusceptible to amoxicillin.

RESULTS

There were 327 patients enrolled in the study. Between 2000 and 2004, vaccine coverage with > or =3 doses of heptavalent pneumococcal vaccine increased from 0% to 54%, but nasopharyngeal carriage of S pneumoniae was stable at 39%. The prevalence of S pneumoniae nonsusceptible to penicillin fell from 25% to 12% among patients, did not vary if <2 years of age, was reduced in children with > or =3 doses of heptavalent pneumococcal vaccine, and increased in child care attendees but reduced in attendees who had > or =3 doses of heptavalent pneumococcal vaccine. The prevalence of S pneumoniae nonsusceptible to amoxicillin in patients remained <5%.

CONCLUSIONS

In our community, widespread use of heptavalent pneumococcal vaccine has reduced the prevalence of S pneumoniae nonsusceptible to penicillin, and the prevalence of S pneumoniae nonsusceptible to amoxicillin remains low (<5%). If antibiotic treatment is elected for children with uncomplicated acute otitis media, we recommend treatment with standard-dose amoxicillin (40-45 mg/kg per day) for children with > or =3 doses of heptavalent pneumococcal vaccine, regardless of age and child care status. High-dose amoxicillin should be used for children with <3 doses of heptavalent pneumococcal vaccine and those treated recently with an antibiotic.

Bacterial etiology of acute otitis media and clinical efficacy of amoxicillin-clavulanate versus azithromycin

BACKGROUND

Acute otitis media (AOM) is one of the most common acute bacterial infection in childhood and also the most frequent reason for outpatient antibiotic therapy. Little recent information about susceptibility patterns of AOM bacterial pathogens in Turkish children has been reported.

OBJECTIVE

To determine the bacterial etiology of acute otitis media in children and to compare the efficiency of 3 days course of azithromycin with a 10 days course of amoxicillin-clavulanate.

METHODS

This prospective, single blind, randomised comparative study was carried out in 180 children with AOM. Paracentesis was performed for middle ear fluid culture before the first dose antibiotic therapy. Children with acute otitis media were randomised to receive either low dose amoxicillin-clavulanate (45/6.4 mg/kg/day in two divided doses for 10 days) or low dose azithromycin (10mg/kg/day for 3 days). Clinical response was assessed on days 2-4, 11-13, 26-28.

RESULTS

Bacterial pathogens were isolated from 108 (60%) of 180 children. Streptococcus pneumoniae was the most common isolated pathogen (39.7%), followed by Haemophilus influenzae (20.7%), Moraxella catarrhalis (15.5%), Staphylococcus aureus (13.8%), Group A beta-hemolytic streptococcus (5.1%), Escherichia coli (3.4%) and Enterococcus faecalis (1.7%). This study demonstrated low resistance rates compared to studies of different countries. Although clinical response rates were better in patients treated with amoxicillin-clavulanate, this was not statistically significant [86.6% (78 of 90)] versus [95.2% (80 of 84)]. Success rates of amoxicillin-clavulanate were high for both S. pneumoniae and H. influenzae. Difference between success rates was not statistically significant (P=0.144 and 0.352).

CONCLUSIONS

Bacteria were isolated in 60% of AOM cases. The clinical efficiency of amoxicillin-clavulanate was found to be equal compared to azithromycin in children with acute otitis media.

Population antibiotic susceptibility for Streptococcus pneumoniae and treatment outcomes in common respiratory tract infections

PURPOSE

Antibiotic-resistant Streptococcus pneumoniae potentially threatens the successful treatment of common respiratory tract infections (RTIs); however, the relationship between antibiotic resistance and treatment outcomes remains unclear. We aimed to test the hypothesis that higher in vitro penicillin and erythromycin nonsusceptibility levels among clinical isolates of S. pneumoniae are associated with higher risk of treatment failure in suppurative acute otitis media (AOM), acute sinusitis, and acute exacerbation of chronic bronchitis (AECB).

METHODS

We conducted a population-level analysis using treatment outcomes data from a national, managed-care claims database, and antibiotic susceptibility data from a national repository of antimicrobial susceptibility results between 1997 and 2000. Treatment outcomes in patients with suppurative AOM, acute sinusitis, or AECB receiving selected macrolides or beta-lactams were assessed. Associations between RTI-specific treatment outcomes and antibiotic nonsusceptibility were determined using Spearman correlation coefficients with condition-specific paired outcome and susceptibility data for each region and each year.

RESULTS

There were 649 552 available RTI outcomes and 7252 susceptibility tests performed on S. pneumoniae isolates. There were no statistically significant trends across time for resolution proportions following treatment by either beta-lactams or macrolides among any of the RTIs. Correlation analyses found no statistically significant association between S. pneumoniae susceptibility and RTI treatment outcomes apart from a significant positive association between of erythromycin nonsusceptibility in ear isolates and macrolide treatment resolution for suppurative AOM.

CONCLUSION

On the population level, in vitro S. pneumoniae nonsusceptibility to macrolide or beta-lactam antibiotics was not associated with treatment failure in conditions of probable S. pneumoniae etiology.

Application of Pharmacokinetics and Pharmacodynamics to Antimicrobial Therapy of Community-Acquired Respiratory Tract Infections

To achieve bacteriologic and clinical success, sufficient concentrations of antimicrobial at the site of infection must be maintained for an adequate period of time. These dynamics are determined by combining drug pharmacokinetic and pharmacodynamic (PK/PD) data with minimum inhibitory concentrations. Bacteriologically confirmed failures have been reported in otitis media and, with a lesser degree of evidence, in pneumococcal pneumonia with a variety of agents that include beta-lactams, macrolides and fluoroquinolones. These failures have been shown to be due to infection by resistant pathogens or suboptimal therapy. However, no clinical failure has been reported during therapy for bacteremic pneumococcal pneumonia with adequate doses of beta-lactams. The failures reported with macrolides or fluoroquinolones have been due to either preexisting resistance to these agents that cannot be overcome by increasing the dose of the antimicrobial or, more rarely, the emergence of resistance during therapy. In this review, we offer an overview of the most important attributes of the main antimicrobials that are currently used in the treatment of community-acquired respiratory tract infections from a PK/PD perspective.

Penicillin susceptibility of pneumococcal isolates causing acute otitis media in children: seasonal variation

BACKGROUND

During the past decade, the prevalence of nonsusceptible Streptococcus pneumoniae strains that cause acute otitis media (AOM) has increased to approximately 30%, and the proportion of fully resistant strains has also increased. The purpose of this study was to determine whether seasonal variation in resistance exists among pneumococcal isolates from children with AOM.

METHODS

Between 1991 and 2003, children 2 months-8 years of age diagnosed with AOM according to stringent criteria underwent tympanocentesis in various clinical trials.

RESULTS

Cultures from 567 of 794 tympanocenteses (71.4%) performed between 1991 and 2003 yielded AOM pathogens. During 1991-1995, only 1 of 43 S. pneumoniae isolates recovered (2%) was nonsusceptible to penicillin. The present analysis focuses on the 691 cultures obtained during 1996-2003; of these, 491 (71.1%) yielded AOM pathogens, of which 165 (33.6%) were S. pneumoniae. Of the pneumococcal isolates, 52 (31.5%) were nonsusceptible to penicillin. The proportion of nonsusceptible strains of S. pneumoniae increased over time: 0 of 3 (0%) in 1996; 2 of 11 (18%) in 1997; 14 of 40 (35%) in 1998; 3 of 34 (9%) in 1999; 11 of 25 (44%) in 2000; 11 of 22 (50%) in 2001; 4 of 18 (22%) in 2002; and 7 of 12 (58%) in 2003 (Cochran Armitage trend test, P = 0.03). AOM caused by nonsusceptible S. pneumoniae was more likely to occur as the winter progressed (P = 0.03); a similar trend was noted for the proportion of nonsusceptible strains that were fully resistant.

CONCLUSIONS

In children with AOM, an increase in the proportion of episodes caused by nonsusceptible S. pneumoniae as the winter months progress may serve as a potential factor in guiding antimicrobial therapy for such children.

Antimicrobial resistance in the nasopharyngeal flora of children with acute otitis media and otitis media recurring after amoxicillin therapy

The objective of this study was to investigate the antimicrobial susceptibility of the organisms isolated from the nasopharynx of children who presented with acute otitis media (AOM) or otitis media that recurred after amoxicillin therapy. Nasopharyngeal cultures obtained from 72 patients, 40 with AOM and 32 with recurrent otitis media (ROM), were analysed. Thirty-six potentially pathogenic organisms were recovered in 34 (85 %) of the children from the AOM group, and 42 were isolated from 29 (91 %) of the children from the ROM group. The organisms isolated were Streptococcus pneumoniae (n = 26), Haemophilus influenzae non-type b (n = 22), Moraxella catarrhalis (n = 13), Streptococcus pyogenes (n = 8) and Staphylococcus aureus (n = 9). Resistance to the eight antimicrobial agents used was found in 37 instances in the AOM group as compared to 99 instances in the ROM group (P < 0.005). The difference between AOM and ROM was significant with Streptococcus pneumoniae resistance to amoxicillin (P < 0.005), to amoxicillin/clavulanate (P < 0.005), to trimethoprim/sulfamethoxazole (P < 0.01), to cefixime (P < 0.01) and to azithromycin (P < 0.01), and for H. influenzae resistance to amoxicillin (P < 0.025). These data illustrate the higher recovery rate of antimicrobial-resistant Streptococcus pneumoniae and H. influenzae from the nasopharynx of children who had otitis media that recurred after amoxicillin therapy than those with AOM.

Emergence of Streptococcus pneumoniae with very-high-level resistance to penicillin

Penicillin resistance threatens the treatment of pneumococcal infections. We used sentinel hospital surveillance (1978 to 2001) and population-based surveillance (1995 to 2001) in seven states in the Active Bacterial Core surveillance of the Emerging Infections Program Network to document the emergence in the United States of invasive pneumococcal isolates with very-high-level penicillin resistance (MIC > or = 8 microg/ml). Very-high-level penicillin resistance was first detected in 1995 in multiple pneumococcal serotypes in three regions of the United States. The prevalence increased from 0.56% (14 of 2,507) of isolates in 1995 to 0.87% in 2001 (P = 0.03), with peaks in 1996 and 2000 associated with epidemics in Georgia and Maryland. For a majority of the strains the MICs of amoxicillin (91%), cefuroxime (100%), and cefotaxime (68%), were > or =8 microg/ml and all were resistant to at least one other drug class. Pneumonia (50%) and bacteremia (36%) were the most common clinical presentations. Factors associated with very highly resistant infections included residence in Tennessee, age of <5 or > or =65 years, and resistance to at least three drug classes. Hospitalization and case fatality rates were not higher than those of other pneumococcal infection patients; length of hospital stay was longer, controlling for age. Among the strains from 2000 and 2001, 39% were related to Tennessee(23F)-4 and 35% were related to England(14-)9. After the introduction of the pneumococcal conjugate vaccine, the incidence of highly penicillin resistant infections decreased by 50% among children <5 years of age. The emergence, clonality, and association of very-high-level penicillin resistance with multiple drug resistance requires further monitoring and highlights the need for novel agents active against the pneumococcus.

Streptococcus pneumoniae: epidemiology and patterns of resistance

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, otitis media, and sinusitis; it results in significant morbidity and mortality in patients with pneumonia and meningitis. The pneumococcus is a common colonizing bacterium in the respiratory tract; it is especially common in the respiratory tracts of children, where it is frequently exposed to antimicrobial agents. This exposure can lead to resistance. Penicillin nonsusceptibility is found in nearly 40% of strains causing disease in adults, although often these cases are treatable with appropriate dosing regimens of many oral and parenteral beta-lactam agents. In the United States resistance to macrolides is widespread--averaging approximately 28%--but geographically variable, ranging from 23% in the northwest to 30% in the northeast. Resistance to tetracyclines and trimethoprim-sulfamethoxazole are reported in approximately 20% and 35% of isolates, respectively, and resistance to multiple classes of agents is increasingly common. Amoxicillin, amoxicillin-clavulanate, respiratory fluoroquinolones, and clindamycin are currently the most effective agents for treatment of respiratory tract infections caused by S pneumoniae, with >90% of isolates in the United States being susceptible. Vancomycin is the only agent against which resistance has not emerged. Patient groups that are at increased risk for developing resistant pneumococcal infections have been identified and include patients with malignancies, human immunodeficiency virus infection, and sickle-cell disease. Judicious use of antimicrobials is the key to preventing the emergence of further resistance, particularly as few new classes of agents are likely to become available for clinical use in the short term.

Developing community-specific recommendations for first-line treatment of acute otitis media: is high-dose amoxicillin necessary?

OBJECTIVES

National recommendations are to use high-dose amoxicillin (80-90 mg/kg per day) to treat uncomplicated acute otitis media (AOM) in children who are at high risk for infection with nonsusceptible Streptococcus pneumoniae (NSSP). However, high-dose treatment may not be necessary if the local prevalence of NSSP is low. The objective of this study was to estimate the local prevalence of NSSP in children with acute upper respiratory illnesses and to develop community-specific recommendations for first-line empiric treatment of AOM.

METHODS

We conducted a cross-sectional prevalence study in the offices of 7 community pediatricians in St Louis, Missouri. S pneumoniae was isolated from nasopharyngeal swabs collected from children who were younger than 7 years and had AOM, nonspecific upper respiratory infection, cough, acute sinusitis, or pharyngitis. Children were excluded from the study when they had received an antibiotic in the previous 4-week period. Parents and providers completed a brief questionnaire to assess risk factors for carriage of NSSP. On the basis of National Clinical Chemistry Laboratory Standards, isolates with a penicillin minimum inhibitory concentration > or =0.12 microg/mL were considered to be nonsusceptible to penicillin (NSSP), and isolates with a penicillin minimum inhibitory concentration >2 microg/mL were categorized as nonsusceptible to standard-dose amoxicillin (35-45 mg/kg per day; NSSP-A).

RESULTS

S pneumoniae was isolated from the nasopharynx of 85 (40%) of 212 study patients (95% confidence interval [CI]: 33%-47%); 41 (48%) of 85 isolates were NSSP (95% CI: 37%-59%), and 6 (7%) were NSSP-A (95% CI: 1.5%-13%). Among the 212 study patients, the prevalence of NSSP was 19% (95% CI: 14%-25%), and the prevalence of NSSP-A was 3% (95% CI: 0.6%-5%). Carriage of NSSP was increased in child care attendees compared with nonattendees (29% vs 14%; odds ratio: 2.6; 95% CI: 1.3-5.2).

CONCLUSIONS

In our community, although the prevalence of NSSP among isolates of S pneumoniae identified from the nasopharynx of symptomatic children is high (48%), the probability of NSSP-A infection among symptomatic children is <5%. Our data support a recommendation to treat most children who have uncomplicated AOM with standard-dose amoxicillin. Children who attend child care or have recently received an antibiotic may require treatment with high-dose amoxicillin. Other communities may benefit from a similar assessment of the prevalence of NSSP and NSSP-A.

Susceptibility of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis to 17 oral antimicrobial agents based on pharmacodynamic parameters: 1998-2001 U S Surveillance Study

Pharmacokinetic/pharmacodynamic parameters were used to interpret susceptibility data for the oral agents tested in a clinically meaningful way. Among S pneumoniae isolates, >99% were susceptible to respiratory fluoroquinolones, 91.6% to amoxicillin, 92.1% to amoxicillin/clavulanic acid (95.2% at the extended-release formulation breakpoint), 90.6% to clindamycin, 80.4% to doxycycline, 71.0% to azithromycin, 72.3% to clarithromycin, 71.8% to cefprozil and cefdinir, 72.6% to cefuroxime axetil, 66.3% to cexime, 63.7% to trimethoprim/sulfamethoxazole, and 19.7% to cefaclor. Among H influenzae isolates, 28.6% were b-lactamase positive, but virtually all were susceptible to amoxicillin/clavulanic acid (98.3%, with 99.8% at the extended-release formulation breakpoint), cexime (100%), and uoroquinolones (99.8%), whereas 93.5% were susceptible to cefdinir, 82.8% to cefuroxime axetil, 78.1% to trimethoprim/sulfamethoxazole, 70.2% to amoxicillin, 25.1% to doxycycline, 23.2% to cefprozil, and 5% to cefaclor, azithromycin and clarithromycin. Most isolates of M catarrhalis were resistant to amoxicillin, cefaclor, cefprozil, and trimethoprim/sulfamethoxazole. Thus significant b-lactam and macrolide/azalide resistance in Streptococcus pneumoniae and b-lactamase production and trimethoprim/sulfamethoxazole resistance in untypeable Haemophilus influenzae are still present. The results of this study should therefore be applied to clinical practice based on the clinical presentation of the patient, the probability of the patient's having a bacterial rather than a viral infection, the natural history of the disease, the potential of pathogens to be susceptible to various oral antimicrobial agents, the potential for cross-resistance between agents with S pneumoniae, and the potential for pathogens to develop further resistance. Antibiotics should be used judiciously to maintain remaining activity and chosen carefully based on activity determined by pharmacokinetic/pharmacodynamic-based breakpoints to avoid these bacteria developing further resistance, particularly to fluoroquinolones.

Mechanisms of resistance among respiratory tract pathogens

Antimicrobial resistance among respiratory tract pathogens represents a significant health care threat. Identifying the antimicrobial agents that remain effective in the presence of resistance, and knowing why, requires a thorough understanding of the mechanisms of action of the various agents as well as the mechanisms of resistance demonstrated among respiratory tract pathogens. The primary goal of antimicrobial therapy is to eradicate the pathogen, via killing or inhibiting bacteria, from the site of infection; the defenses of the body are required for killing any remaining bacteria. Targeting a cellular process or function specific to bacteria and not to the host limits the toxicity to patients. Currently, there are four general cellular targets to which antimicrobials are targeted: cell wall formation and maintenance, protein synthesis, DNA replication, and folic acid metabolism. Resistance mechanisms among respiratory tract pathogens have been demonstrated for all four targets. In general, the mechanisms of resistance used by these pathogens fall into one of three categories: enzymatic inactivation of the antimicrobial, prevention of intracellular accumulation, and modification of the target site to which agents bind to exert an antimicrobial effect. Resistance to some agents can be overcome by modifying the dosage regimens (e.g., using high-dose therapy) or inhibiting the resistance mechanism (e.g., b-lactamase inhibitors), whereas other mechanisms of resistance can only be overcome by using an agent from a different class. Understanding the mechanisms of action of the various agents and the mechanisms of resistance used by respiratory tract pathogens can help clinicians identify the agents that will increase the likelihood of achieving optimal outcomes.

Use of oral cephalosporins in the treatment of acute otitis media in children

The selection of the most effective antimicrobial to treat acute otitis media (AOM) has become more difficult in recent years because of increasing antibiotic resistance among all AOM pathogens. Resistance of Streptococcus pneumoniae to penicillin as well as amoxicillin ranges from 30 to 55% in the USA. Currently, 40-55% of Haemophilus influenzae and 90-100% of Moraxella catarrhalis are resistant to penicillin because of the production of Beta-lactamases. This review discusses the availability of oral cephalosporins that can be utilised for the treatment of AOM in children. An evaluation is made regarding their in vitro activity against the pathogens, their middle-ear concentrations, pharmacokinetics and pharmacodynamics (PK/PD). The cephalosporins that will be discussed are cefuroxime-axetil, cefprozil, cefdinir and cefpodoxime-proxetil. The current recommendations for therapy of AOM limit the choices of clinicians to a single cephalosporin (cefuroxime-axetil). However, clinical, bacteriological and PK/PD data shows that several other cephalosporins (cefprozil, cefdinir and cefpodoxime-proxetil) possess similar indices which provide the clinician with wider therapeutic choices that can insure better compliance and ultimately better success in eradication of the infection.

Antibacterial resistance among children with community-acquired respiratory tract infections (PROTEKT 1999-2000)

OBJECTIVE

To determine the susceptibility of bacterial respiratory tract pathogens, isolated from children (0-12 years) as part of the global PROTEKT surveillance study (1999-2000), to a range of antibacterials, including the ketolide telithromycin.

METHODS

Minimum inhibitory concentrations of the antibacterials studied were determined at a central laboratory using the NCCLS microdilution broth method. Macrolide resistance mechanisms were detected by PCR.

RESULTS

Of 779 Streptococcus pneumoniae isolates worldwide, 43% were non-susceptible to penicillin (18% intermediate; 25% resistant) and 37% were resistant to erythromycin, with considerable intercountry variation. Eighteen per cent of 653 Haemophilus influenzae and >90% of 316 Moraxella catarrhalis isolates produced beta-lactamase. Of 640 Streptococcus pyogenes isolates, 10% were resistant to erythromycin, with considerable intercountry variation. All S. pneumoniae and 99.8% of H. influenzae isolates were susceptible to telithromycin using breakpoints proposed to the NCCLS (<or=1 and <or=4 mg/L, respectively). All M. catarrhalis and 97% of S. pyogenes and isolates were susceptible to <or=1 mg/L telithromycin.

CONCLUSIONS

Antibacterial resistance complicates the empirical treatment of respiratory tract infections in children and requires continued monitoring. Telithromycin may be a useful therapeutic alternative as it is highly active against strains exhibiting various resistance phenotypes.

Antimicrobial resistance among pediatric respiratory tract infections: clinical challenges

Considerable development of antimicrobial resistance has occurred in the major pediatric bacterial pathogens, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. However, most of the respiratory infections that children suffer are viral and self-limiting, and only a small percentage of them will develop secondary bacterial infections with the pathogens listed. The challenge for rational antibiotic use is to determine which patients can be treated conservatively and which require antimicrobial intervention to avoid prolonged discomfort or development of permanent sequelae. The basis for rational use of antibiotic in the era of resistance in these major pathogens is to avoid overuse of antimicrobial agents, tailor treatment to identified pathogens as much as possible, and base empiric treatment on the disease being treated and the susceptibility of the probable pathogens at breakpoints based on pharmacokinetic and pharmacodynamic parameters. With appropriate dosing regimens based on these parameters and despite development of resistance, amoxicillin is still one of the most active oral agents against S. pneumoniae and non-beta-lactamase producing strains of H. influenzae, whereas amoxicillin-clavulanate is active against beta-lactamase-producing strains of H. influenzae and M. catarrhalis. Parenteral ceftriaxone and oral and parenteral fluoroquinolones are active against all 3 species, but fluoroquinolones should be used with utmost caution when all other options have been considered because of concerns about toxicity and development of resistance. Introduction of a 7-valent conjugate pneumococcal vaccine in the United States in 2000 reduced the prevalence of invasive pneumococcal disease in children younger than 2 years old, but, as of 2001, had not had a major impact on decreasing antimicrobial resistance.

Aggregated antibiograms and monitoring of drug-resistant Streptococcus pneumoniae

Community-specific antimicrobial susceptibility data may help monitor trends among drug-resistant Streptococcus pneumoniae and guide empiric therapy. Because active, population-based surveillance for invasive pneumococcal disease is accurate but resource intensive, we compared the proportion of penicillin-nonsusceptible isolates obtained from existing antibiograms, a less expensive system, to that obtained from 1 year of active surveillance for Georgia, Tennessee, California, Minnesota, Oregon, Maryland, Connecticut, and New York. For all sites, proportions of penicillin-nonsusceptible isolates from antibiograms were within 10 percentage points (median 3.65) of those from invasive-only isolates obtained through active surveillance. Only 23% of antibiograms distinguished between isolates intermediate and resistant to penicillin; 63% and 57% included susceptibility results for erythromycin and extended-spectrum cephalosporins, respectively. Aggregating existing hospital antibiograms is a simple and relatively accurate way to estimate local prevalence of penicillin-nonsusceptible pneumococcus; however, antibiograms offer limited data on isolates with intermediate and high-level penicillin resistance and isolates resistant to other agents.

Prevention and management of antibacterial resistance for primary care patients with respiratory tract infections

This review examines the problem of increasing antibacterial resistance among the pathogens commonly associated with community-acquired respiratory tract infections, particularly Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. The increases in morbidity, mortality, and treatment cost associated with increased resistance to available antibiotics are challenging prescribers to find more effective therapeutic strategies. A MEDLINE search of the literature from 1966 to the present was performed to seek data relevant to the issue of resistance, especially the negative effects on patient outcomes and costs of therapy. Several observations and conclusions emerged. Data are lacking on local resistance patterns, broad-spectrum agents are overprescribed when narrower-spectrum choices would be more appropriate, a need exists for educational programs to encourage restricting drug use and changing prescribing habits, and there is a need for new antibiotic choices. The best antibiotic options are agents with a tailored spectrum of activity that are targeted at particular respiratory tract pathogens and have low potential to select for resistant organisms.

Bacteriologic and clinical efficacy of oral gatifloxacin for the treatment of recurrent/nonresponsive acute otitis media: an open label, noncomparative, double tympanocentesis study

BACKGROUND

Gatifloxacin is an 8-methoxyfluoroquinolone with good activity against respiratory pathogens.

OBJECTIVES

To document the bacteriologic and clinical efficacy of gatifloxacin in recurrent/nonresponsive acute otitis media (AOM).

METHODS

One hundred sixty patients 6 to 48 months of age with recurrent/nonresponsive AOM received gatifloxacin suspension (10 mg/kg once daily for 10 days). Recurrent AOM was defined as > or =3 AOM episodes during the previous 6 months or > or =4 AOM episodes during the previous 12 months. Nonresponsive AOM was defined as AOM occurring < or =14 days after completing antibiotic treatment or not improving after > or =48 h of therapy. Middle ear fluid (MEF) obtained by tympanocentesis pretreatment (Day 1) and 3 to 5 days after initiation of treatment (Days 4 to 6) was cultured. Additional MEF cultures were obtained if clinical failure or recurrence of AOM occurred. Bacteriologic failure was defined by culture-positive MEF during treatment. Patients were followed until Days 22 to 28. Susceptibility was determined by broth microdilution.

RESULTS

One hundred twenty-eight (80%) patients completed treatment, and 32 discontinued the study prematurely (adverse events, 17; lost to follow-up, 10; consent withdrawal, 3; and laboratory abnormalities, 2). From 89 patients (median age, 1 year; median number of prior AOM episodes, 4; range, 0 to 12), 121 pathogens were recovered: Haemophilus influenzae, 74 (61%); Streptococcus pneumoniae, 36 (30%); Moraxella catarrhalis, 9 (7%); and Streptococcus pyogenes, 2 (2%). The 36 S. pneumoniae isolates were susceptible to gatifloxacin (MIC50 0.25 microg/ml); 26 of 36 (72%) were penicillin-nonsusceptible (15 fully resistant). All 74 H. influenzae isolates were susceptible to gatifloxacin (MIC < or = 0.03 mg/ml). Fourteen of 74 (19%) and 9 of 9 (100%) H. influenzae and M. catarrhalis isolates, respectively, produced beta-lactamase. Bacteriologic eradication was achieved for 118 of 121 (98%) pathogens: 74 of 74 H. influenzae; 34 of 36 (94%) S. pneumoniae; 9 of 9 M. catarrhalis; and 1 of 2 S. pyogenes. Clinical improvement/cure at end of treatment was seen in 103 of 114 (90%) clinically evaluable patients. Clinical recurrence of AOM after completion of therapy occurred in 31 patients. Of the 27 recurrent AOM cases in which tympanocentesis was performed, there were 16 (59%) new infections, 4 (15%) culture-negative results and only 7 (26%) true bacteriologic relapses. Adverse events were recorded in 21 of 160 (13%) patients: vomiting, 16; diarrhea, 3; maculopapular rash, 2. No articular adverse events were recorded.

CONCLUSION

Gatifloxacin is efficacious and safe for the treatment of recurrent/nonresponsive AOM.

Shortened course of antibacterial therapy for acute otitis media

Acute otitis media (AOM) is the most frequent bacterial disease and leading cause of antibacterial prescriptions in infants and children. Although AOM resolves spontaneously in most patients, antibacterial treatment is believed to be indicated in most industrial countries, particularly for infants, to prevent severe complications and relieve symptoms more rapidly. The classical duration of oral antibacterial therapy has been 10 days. During the last decade, the efficacy of shortened course antibacterial therapy has been demonstrated in many trials. Advantages of shorter treatment periods include less expense, better compliance, and potentially less impact on the commensal flora. However, short course antibacterial therapy may not be appropriate for children <2 years of age, particularly those attending daycare centers, those with otorrhea or a recent episode (<1 month), and otitis-prone children. Reasons for a poorer efficacy in these groups of children are still not completely understood.

Recurrent acute otitis media occurring within one month from completion of antibiotic therapy: relationship to the original pathogen

OBJECTIVES

(1) To determine the relationship between acute otitis media (AOM) pathogens isolated in cases of early clinical recurrence of AOM (occurring within 1 month from completion of therapy) to the original pathogens causing the initial AOM episode; and (2) To determine whether shorter time intervals between completion of antibiotic therapy and clinical recurrences of AOM are associated with higher rates of true bacteriologic relapse.

PATIENTS AND METHODS

From 1995 through 2000, 1077 infants and young children ages 3 to 36 months with AOM were enrolled in double tympanocentesis (performed on Day 1 in all patients and Days 4 to 6 in those initially culture-positive) studies. Of these, 834 (77%) completed successfully the antibiotic treatment [pathogen eradication on Days 4 to 6 of therapy or no pathogen on middle ear fluid (MEF) culture on Day 1 and clinical improvement at end of therapy]. Patients were followed for 3 to 4 weeks after completion of therapy, and additional MEF cultures were obtained if clinical recurrence occurred. True bacteriologic relapse was defined as the presence of a pathogen identical with that isolated before therapy by serotype and pulsed field gel electrophoresis for and by pulsed field gel electrophoresis for Streptococcus pneumoniae and beta-lactamase production for Haemophilus influenzae.

RESULTS

MEF cultures were performed in 108 consecutive patients with early recurrent AOM. One hundred pathogens were isolated at recurrence in 88 of 108 (81%) patients: 54 H. influenzae; 45 S. pneumoniae; and 1 Moraxella catarrhalis. Most recurrent AOM episodes developed during the first 2 weeks of follow-up; 39 (36%), 38 (35%), 21 (19%) and 10 (9%) recurrent AOM episodes occurred on Days 1 to 7, 8 to 14, 15 to 21 and 22 to 28 after completion of therapy, respectively. In most patients these episodes were caused by a new pathogen. True bacteriologic relapses were found in 30 (28%) of 108 patients whose MEF cultures were positive for 35 pathogens: 13 of 108 (12%) S. pneumoniae; 12 of 108 (11%) H. influenzae; and 5 of 108 (5%) both. When timing of recurrent AOM after completion of therapy was analyzed, true bacteriologic relapses were found in 16 of 39 (41%), 10 of 38 (26%), 3 of 21 (14%) and 1 of 10 (10%) of all episodes on Days 1 to 7, 8 to 14, 15 to 21 and 22 to 28 after completion of therapy, respectively (P = 0.01). The respective rates for were 11 of 17 (65%), 3 of 10 (30%), 3 of 13 (23%) and 1 of 5 (20%) (P = 0.02). For H. influenzae the respective rates were 8 of 19 (42%), 9 of 23 (39%), 0 of 8 (0%) and 0 of 4 (0%) (P = 0.02).

CONCLUSIONS

Most recurrent AOM episodes occurring within 1 month from completion of antibiotic therapy are in fact new infections. Most of the true bacteriologic AOM relapses occur within 14 days after completion of therapy, but even during this time interval most of the recurrences are caused by new pathogens. H. influenzae is very unlikely to cause true bacteriologic AOM relapses 14 days or later after completion of therapy.

Health care resource utilization associated with treatment of penicillin-susceptible and -nonsusceptible isolates of Streptococcus pneumoniae

Despite failure to correlate in vitro susceptibility with clinical outcomes for respiratory tract infections and bacteremia, resistance affects management of patients with pneumococcal infections. The economic impact of resistance among pneumococci has not been evaluated. We conducted a single-center, retrospective, observational, cohort study of hospitalized patients infected with Streptococcus pneumoniae isolated from blood or a respiratory source between January 1, 1995, and December 31, 1998. Data were collected for 36 days surrounding the day that the first positive culture was collected. Patients were grouped according to isolate penicillin-susceptibility profile [susceptible minimum inhibitory concentration (MIC) < or = 0.06 microg/ml, nonsusceptible MIC > or = 0.125 microg/ml), and data were analyzed with respect to health care resource utilization patterns. Of 231 patients identified, 142 and 89 had susceptible and nonsusceptible isolates, respectively. Groups were similar with respect to demographics and comorbidities, except that patients infected with a nonsusceptible isolate were more likely to have the isolate obtained from a respiratory source and to have a history of recent antibiotic therapy. No difference was noted with respect to clinical outcome; however, patients infected with a nonsusceptible isolate had a longer median stay (14 vs 10 days, p<0.05). They also had significantly higher total median costs (1600 dollars, 95% confidence interval 257-2943 dollars) due to room and nursing services. Infections caused by penicillin-nonsusceptible pneumococci were not associated with a worse outcome in hospitalized patients but were associated with increased cost of care.

Achieving bacterial eradication using pharmacokinetic/pharmacodynamic principles

Evidence from studies in otitis media indicates that antimicrobials and dosing regimens that have equivalent bacteriologic efficacy against susceptible pathogens can have significantly different bacteriologic success rates against resistant strains of the same species. Unlike macrolide and fluoroquinolone resistance, penicillin resistance can be overcome in Streptococcus pneumoniae by increasing the dose, and hence increasing the time for which the serum concentrations are above the MIC. The new clinical formulation of extra-strength amoxicillin-clavulanate provides 90 mg/kg per day amoxicillin plus 6.4 mg/kg per day clavulanate (14:1) divided every 12 h, compared with 45/6.4 mg/kg per day b.i.d. with conventional dosing. The pharmacokinetic/pharmacodynamic (PK/PD) profiles of extra-strength amoxicillin-clavulanate predict that the new formulation will be more effective than the conventional formulation against S. pneumoniae with elevated amoxicillin MICs and against Haemophilus influenzae. In an open-label, non-comparative study in children with acute otitis media, the extra-strength formulation had high bacteriologic success rates against the major respiratory pathogens, including penicillin-resistant S. pneumoniae. The development of new antimicrobial agents and formulations should be aimed at meeting PK/PD parameters predictive of bacterial eradication of both susceptible and resistant strains.

Bacterial resistance--the clinical challenge

Resistance to antibacterial agents has increased among many species of bacterial pathogens in the last two decades. While this has been recognized and has been a matter of concern among those concerned with infectious diseases, it is only relatively recently that prescribing physicians have become aware of the problem. A range of official bodies, both national and international, have proposed a range of strategies for controlling this increase in resistance. The relationship between resistance and clinical efficacy or failure is unclear in many areas, although increasingly resistance can be seen to be associated with a less than optimal clinical response. Although the relationship between antibiotic use and resistance is complex, there is an assumption that excessive use of antibacterials may drive an increase in resistance. The term 'prudent prescribing' is frequently used in official documents, but it is not easy for the prescriber to determine exactly what is prudent prescribing. There have been efforts to reduce the unnecessary use of antibacterials in the treatment of many community respiratory infections where the etiological agent is likely to be viral. Guidelines for prescribing have been drawn up by governments and professional societies but their impact can be variable. They need to take account of the changing patterns of resistance, for example the rise in high-level penicillin resistance among pneumococci. They also need to be readily accessible to the practicing clinician. Surveillance systems are available in abundance and these may be local, national, or international. They often, however, suffer from drawbacks and are frequently selective. Frequently the prescriber does not have ready access to the most appropriate data. Integrated strategies to control resistance are urgently needed, as are improved rapid diagnostic facilities.

Suboptimal antibiotic dosage as a risk factor for selection of penicillin-resistant Streptococcus pneumoniae: in vitro kinetic model

Optimizing pharmacokinetic/pharmacodynamic indices of antibiotics to obtain clinical and microbiological efficacy is essential, but dosing regimens must also be tailored to minimize the risk for emergence of resistance. The aim of the present study was to investigate whether certain concentrations of benzylpenicillin are critical for the selection of resistant subpopulations. A mixed culture of Streptococcus pneumoniae containing ca. 90% susceptible (MIC = 0.031 mg/liter), 9% intermediate (MIC = 0.25 mg/liter), and 1% resistant (MIC = 8 mg/liter) was studied in an in vitro kinetic model. The time that concentrations exceeded the MIC (T>MIC) for the three strains in the culture was varied by different initial concentrations of benzylpenicillin. Samples for viable counts were withdrawn at different times during 24 h and seeded on blood agar plates and on selective antibiotic-containing plates. The T>MIC varied from 46 to 100% for the susceptible strain, from 6 to 100% for the intermediate strain, and from 0 to 48% for the resistant strain. Our study, which may mimic the clinical situation with carriage of a mixed population of S. pneumoniae with different antibiotic susceptibilities, has shown that selection of resistant bacteria may easily occur if dosing regimens are only targeted toward fully susceptible strains.

A critical assessment of published guidelines and other decision-support systems for the antibiotic treatment of community-acquired respiratory tract infections

Guidelines are an important means by which professional associations and governments have sought to improve the quality and cost-effectiveness of disease management for infectious diseases. Prescribing of initial antibiotic therapy for community-acquired respiratory tract infections (RTIs) is primarily empiric and physicians may often have a limited appreciation of bacterial resistance. Recent guidelines for managing RTIs have adopted a more evidence-based approach. This process has highlighted important gaps in the existing knowledge base, e.g. concerning the impact of resistance on the effectiveness of oral antibiotics for outpatient community-acquired pneumonia and the level of resistance that should prompt a change in empiric prescribing. In upper RTIs, the challenge is to identify patients in whom antibiotic therapy is warranted. Concentrated, sustained efforts are needed to secure physicians' use of guidelines. The information should be distilled into a simple format available at the point of prescribing and supported by other behavioral change techniques (e.g. educational outreach visits). Advances in information technology offer the promise of more dynamic, computer-assisted forms of guidance. Thus, RTI prescribing guidelines and other prescribing support systems should help control bacterial resistance in the community. However, their effect on resistance patterns is largely unknown and there is an urgent need for collaborative research in this area. Rapid, cost-effective diagnostic techniques are also required and new antibiotics will continue to have a role in disease management.

Bacterial eradication in the treatment of otitis media

Drugs differ in their ability to eradicate various pathogens from the middle-ear cavity during acute otitis media (AOM), and these differences clearly affect clinical outcome. Outcome is derived from differences in the association between concentrations of the drugs at the site of infection and the antimicrobial effect (termed pharmacodynamics). These differences are even more marked in the present era of antimicrobial resistance. However, since AOM is a self-limiting disease in most cases, difference in clinical outcome is more difficult to ascertain than that of bacteriological outcome, which is measured within 3-5 days. A favourable clinical outcome regardless of the bacteriological effect of the drug can result in false optimism when less-effective antibiotic drugs are used. Inappropriate study design and manipulation of clinical results add to this confusion. In this review we attempt to highlight the evidence regarding bacteriological response to antibiotics in AOM and to draw attention to potential flaws that may mislead clinicians.

Effects of various test media on the activities of 21 antimicrobial agents against Haemophilus influenzae

As considerable variation in the antimicrobial susceptibility of Haemophilus influenzae has been reported, the effects of various test media on the susceptibility of H. influenzae were studied. MICs were determined by three laboratories for 21 antimicrobial agents against a panel of 100 selected isolates. Testing was performed using a reference NCCLS frozen broth microdilution method with Haemophilus test medium (HTM) broth and dried commercial MIC trays rehydrated with the following media: in-house and commercially prepared HTM broth, Mueller-Hinton broth with 2% lysed horse blood and NAD, IsoSensitest broth with 2% lysed horse blood and NAD, and IsoSensitest broth-based HTM. Overall, all results were very reproducible, with the MIC at which 50% of the isolates tested are inhibited (MIC(50)), MIC(90), and geometric mean MIC being within one doubling dilution by all six methods and at all three testing centers for 15 of the 21 agents tested. Interlaboratory differences were more marked than intralaboratory differences or differences among media. Cefprozil, cefaclor, and trimethoprim-sulfamethoxazole results differed the most, while results for ampicillin, amoxicillin-clavulanic acid, cefdinir, cefixime, ceftriaxone, and clarithromycin were the most reproducible. However, these variations in results caused considerable differences in susceptibility rates for agents for which NCCLS susceptible breakpoints were close to the geometric mean MIC, particularly for cefaclor and cefprozil. This was much less of a problem when pharmacokinetic-pharmacodynamic breakpoints were used. Reproducible susceptibility results were obtained for a wide range of agents against H. influenzae in three laboratories using a variety of media that support the growth of this fastidious species.

Association between antimicrobial resistance among pneumococcal isolates and burden of invasive pneumococcal disease in the community

Treatment of infections with drug-resistant strains of Streptococcus pneumoniae (pneumococcus) may fail; whether drug resistance is associated with an increase in the number of serious infections in the community is unknown. We evaluated the relationship between the proportion of antimicrobial-resistant S. pneumoniae isolates and the number of cases of invasive pneumococcal disease. Linear regression models included 1996 county-level data from 38 counties participating in the US Centers for Disease Control and Prevention's Active Bacterial Core Surveillance. Separate models evaluated hospitalized children aged <5 years, nonhospitalized children aged <5 years, adults aged 18-64 years, and adults aged >64 years. The proportion of isolates resistant to > or =3 drug classes was associated with invasive disease in both hospitalized (P=.06) and nonhospitalized (P=.001) children. The proportion of multidrug-resistant pneumococcal isolates did not predict invasive cases among adults. The increasing prevalence of multidrug-resistant pneumococci among children may be leading to an increase in invasive disease.

Dynamics of pneumococcal nasopharyngeal carriage in children with nonresponsive acute otitis media treated with two regimens of intramuscular ceftriaxone

BACKGROUND

A 3-day intramuscular ceftriaxone regimen was superior to a 1-day regimen in the treatment of nonresponsive acute otitis media caused by resistant Streptococcus pneumoniae. However, the effect of various regimens of intramuscular cefriaxone on the nasopharyngeal carriage of S. pneumoniae and especially that of resistant strains during and after therapy has not been thoughtfully studied.

OBJECTIVES

To compare the effect of one dose and three dose intramuscular ceftriaxone regimens on the nasopharyngeal carriage of S. pneumoniae in patients with nonresponsive acute otitis media treated with these two regimens and to document the dynamics of nasopharyngeal colonization with S. pneumoniae during and after completion of these two therapeutic regimens.

PATIENTS AND METHODS

In a prospective study performed during January, 1998, through September, 1999, 170 evaluable patients ages 3 to 36 months with nonresponsive acute otitis media were randomized to receive the 1 (n = 83)- or 3 (n = 87)-day intramuscular ceftriaxone regimen (50 mg/kg/day), respectively. Nasopharyngeal cultures for S. pneumoniae were obtained on Days 1, 4 to 5, 11 to 14 and 28 to 30. Susceptibility of S. pneumoniae to penicillin and ceftriaxone was determined by E-test.

RESULTS

On Day 1 nasopharyngeal S. pneumoniae carriage was found in 108 (64%) patients, 54 in each treatment group. Forty-seven of 54 (87%) and 9 of 54 (17%) S. pneumoniae isolates from the one dose group were nonsusceptible to penicillin and ceftriaxone, respectively; the respective values in the three dose group were 49 of 54 (91%) and 8 of 54 (15%). On Days 4 and 5 negative nasopharyngeal cultures were achieved in 43 of 83 (52%) and 70 of 87 (80%) cases from the one dose and three dose group, respectively (P < 0.001). Eradication of penicillin-nonsusceptible S. pneumoniae was achieved on Day 4 to 5 in 18 of 49 (37%) and 39 of 49 (80%) organisms isolated from the one dose and three dose groups, respectively (P < 0.001). Nasopharyngeal S. pneumoniae carriage among evaluable patients on Days 11 to 14 and Days 28 to 30 was 43 of 69 (62%) and 31 of 45 (69%) for the one dose group and 42 of 73 (58%) and 31 of 50 (62%) for the three dose group, respectively (P not significant). A decrease was observed during the study period in the proportion of highly penicillin-resistant S. pneumoniae isolated in the three dose group compared with the one dose group (30, 24, 17 and 13% vs. 30, 27, 19 and 26% at Days 1, 4 to 5, 11 to 14 and 28 to 30, respectively; P = 0.05).

CONCLUSIONS

A marked reduction in the carriage of penicillin-nonsusceptible S. pneumoniae (including highly penicillin-resistant organisms) was achieved on Days 4 to 5 of therapy with both ceftriaxone regimens. The 3-day intramuscular ceftriaxone regimen was significantly superior to the 1-day regimen in the reduction of carriage during the treatment period. The reduction of overall S. pneumoniae nasopharyngeal carriage by both ceftriaxone regimens was a short-lived phenomenon followed by rapid recolonization of the nasopharynx.

Appropriate use of antimicrobials for drug-resistant pneumonia: focus on the significance of beta-lactam-resistant Streptococcus pneumoniae

The beta-lactam antibiotics (penicillins and cephalosporins) are commonly prescribed for the treatment of community-acquired pneumonia. However, Streptococcus pneumoniae, the most common etiologic agent of community-acquired pneumonia, has become increasingly resistant to beta-lactams over the past decade. The results of several studies suggest that penicillins remain effective for streptococcal pneumonia when the infecting pathogen has a minimal inhibitory concentration (MIC) </=2 microgram/mL, presumably because the pharmacokinetic and pharmacodynamic parameters associated with current dosing regimens are still sufficient. However, when the MIC >/=4 microgram/mL, increased rates of mortality (for patients who survive their first 4 days of hospitalization) may occur. Currently, 3.5%-7.8% of S. pneumoniae clinical isolates have MICs that fall in this latter class, but these rates may rise in the future. The clinical relevance of in vitro resistance may be related to at least 3 factors: concordance of antimicrobial therapy, severity of illness, and virulence.