The effect of changes in the consumption of macrolide antibiotics on erythromycin resistance in group A streptococci in Finland. Finnish Study Group for Antimicrobial Resistance

Clonally related penicillin-nonsusceptible Streptococcus pneumoniae serotype 14 from cases of meningitis in Salvador, Brazil

Active hospital-based surveillance in the city of Salvador, Brazil, from December 1995 through October 1998, identified 221 patients with confirmed pneumococcal meningitis. Of these 221 patients, 29 (13%) had isolates with intermediate-level resistance to penicillin. Infection with these penicillin-nonsusceptible isolates was significantly associated with age of <2 years (P<.0019), previous antibiotic use (P<.0006), and coresistance to trimethoprim-sulfamethoxazole (P<.0000). Serotype 14 was the most prevalent serotype (55.2%) of penicillin-nonsusceptible isolates. Strain typing by repetitive element BOX polymerase chain reaction (PCR) analysis showed that penicillin-nonsusceptible serotype 14 isolates had closely related BOX PCR patterns, whereas penicillin-susceptible serotype 14 isolates each had distinct, unrelated patterns. Penicillin-nonsusceptible serotype 14 isolates from Salvador and other Brazilian cities had similar BOX PCR patterns. These observations indicate that in Brazil a large proportion of cases of penicillin-nonsusceptible pneumococcal meningitis appear to be caused by a closely related group of serotype 14 strains that may have disseminated to widely separate geographic areas.

Does clinical error contribute to unnecessary antibiotic use?

Patient expectations and physician attitudes are often cited as factors in the overuse of antibiotics. This study examined whether clinical error might also be important. In treating 517 patients with sore throat, family physicians estimated the probability that group A streptococcus infection was present. Two thirds of antibiotics prescribed were to culture-negative patients and therefore considered unnecessary. Physicians overestimated the probability that a group A streptococcal infection was present by an average 33.2% in these cases, compared with 6.9% otherwise (p < 0.001). The rate of unnecessary prescribing was 5.1% when the physician estimate differed from the true probability of a group A streptococcal infection by <10%, 16.0% for an error of 10-29%, 35.6% for an error of 30-49%, and 78.3% when the chance of the infection was overestimated by 50% or more. Clinical error in estimating the likelihood of group A streptococcal infection probably contributes to unnecessary antibiotic use in patients with sore throat.

Susceptibility of group A beta-hemolytic streptococci to thirteen antibiotics: examination of 301 strains isolated in the United States between 1994 and 1997

BACKGROUND

Because of continuing reports from many countries of increasing resistance of group A streptococci to macrolide antibiotics, we determined the antibiotic susceptibility of recent group A streptococcal isolates from the United States.

METHODS

We evaluated 301 Streptococcus pyogenes isolates (245 from patients with uncomplicated pharyngitis and 56 isolates from patients with invasive systemic infections) for susceptibility using the Etest technique. The isolates came from 24 states and the District of Columbia during the years 1994 through 1997. Thirteen antibiotics (azithromycin, ceftriaxone, cephalothin, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, imipenem, levofloxacin, oxacillin, penicillin G, tetracycline and trimethoprim-sulfamethoxazole) were studied.

RESULTS

The MIC90 for penicillin was 0.016 microg/ml, which is not significantly different from previous reports. Of the 301 isolates only 2.6% were resistant to a macrolide antibiotic and only 4% were resistant to tetracycline.

CONCLUSIONS

These data indicate that antibiotic resistance among recent isolates of group A streptococci (including those from patients with severe infections) currently is not a clinically significant problem in the United States.

Antibiotic resistance in Streptococcus pneumoniae isolated from children

OBJECTIVE

To determine the level of antibiotic resistance in pneumoniae (S. pneumoniae) isolated from nasal swabs of healthy children.

METHOD

Cross-sectional community survey.

SETTING

Survey was undertaken in general practice settings in Canberra during March and April 1998.

SUBJECTS

Four hundred and sixty-one children under 3 years of age enrolled in general practice trial of clinical practice guidelines for antibiotic use.

OUTCOME MEASURES

Resistance to penicillin, erythromycin, co-trimoxazole, tetracycline, chloramphenicol and cefotaxime among the isolates of S. pneumoniae.

RESULTS

A total of 461 nasal swabs were collected and S. pneumoniae was isolated from 171 (37.1%). Penicillin resistance was found in 12.3% of these isolates, with high level resistance in 0.6%. Resistance rates were higher for cotrimoxazole (44.4%) and erythromycin (18.1%) than for penicillin. Multidrug resistance was found in 19% of these isolates. There was a significant association between the attendance at a day care centre and carriage of pneumococcus (53% vs 32%, odds ratio (OR) 2.4, 95% confidence interval (CI) 1.5-3.7, P < 0.001). Children who attended day care centers and had received antibiotics during the 4 months prior to swab collection were three times more likely to carry an antibiotic-resistant isolate than children who had neither attended a day care centre nor received antibiotics (68% vs 40%, OR 3.1, 95% CI 1.2-8.4, P = 0.02).

CONCLUSION

The level of antibiotic resistance in pneumococci from healthy children was of concern. Carriage of pneumococcus was significantly higher in children who attended a day care centre. Resistance was significantly correlated with antibiotic use in combination with day-care attendance. These findings warrant more judicious use of antibiotics in children.

Alterations in the conjunctival bacterial flora following a single dose of azithromycin in a trachoma endemic area

BACKGROUND/AIMS

The World Health Organisation has recommended repeated mass treatment of children in trachoma endemic areas with oral azithromycin. While chlamydia, the causative agent of trachoma, remains universally sensitive to azithromycin, there is concern that large scale programmes may alter the bacterial flora and induce resistance in streptococcal species. In this study the effect of a single dose of azithromcyin on the prevalence, species distribution, and resistance of conjunctival bacterial flora was determined.

METHODS

Baseline and 14 day follow up bacterial cultures were taken from the conjunctivae of 121 children who reside in a trachoma endemic area of Nepal. 91 children were treated with azithromycin at baseline and 31 children received deferred treatment at the 14 day follow up.

RESULTS

Although the prevalence of bacterial pathogens decreased significantly with azithromycin treatment, a significant change in the distribution of specific bacterial pathogens could not be demonstrated. Streptococcal resistance to azithromycin was found significantly more frequently after treatment. No change in the prevalence, distribution, or resistance pattern was found in the untreated control group.

CONCLUSION

Repeated mass treatment of trachoma endemic areas with oral azithromycin will have an effect on bacterial flora. However, further work needs to be done to determine if this will have any clinical relevance.

Bacterial resistance and antibiotic use in the emergency department

Antibiotic resistance among bacteria that are commonly encountered in the pediatric emergency department is a fact of nature. New antibiotics will provide some help, but probably only temporarily. Vaccine strategies seem to provide the best answer to resistance, and many physicians eagerly await the conjugated pneumococcal vaccines, which we can only hope to be as successful as the H. influenzae type b vaccines. Vaccines against other resistant organisms are likely further off. At this point, a major goal must be to limit the prevalence of antibiotic resistance. In considering this goal, two complementary strategies are key. The first is to avoid antibiotics in situations in which they are unlikely to provide benefit, such as for colds, URIs, and bronchitis. The second is to use narrow-spectrum antibiotics as much as possible to minimize selective pressure. Emerging evidence shows that these strategies can be effective. In a day-care center in Omaha, Nebraska, Boken et al showed that nasopharyngeal carriage of highly resistant S. pneumoniae decreased dramatically among attendees when antibiotic use decreased. In Iceland, a nationwide campaign that resulted in decreased antibiotic use was followed by a decrease in the incidence of penicillin-resistant pneumococcal infections from 20.0% to 16.9% and a decrease in the rate of carriage of resistant pneumococci among day-care-center attendees from 49% to 15%. In Finland, erythromycin resistance in Group A streptococci recovered from pharyngeal and pus samples had reached 13% in 1990. National guidelines that recommended a reduction in the use of erythromycin and other macrolide antibiotics in the treatment of outpatients with respiratory and skin infections were instituted, and by 1996, macrolide antibiotic consumption had decreased by 50%, with a similar 50% decrease in frequency of erythromycin-resistant isolates. In the absence of such national strategies, it is incumbent on physicians treating infections on a daily basis in the emergency department to consider carefully the judicious use of antibiotics.

Multiple prescriptions of antibiotics for children aged 0 to 5 years in relation to type of antibiotic

The risk of receiving more than one prescription within an antibiotic course was examined for all children aged 0 to 5 years in a Danish county during 1997. We identified 29,307 prescriptions of systemic antibiotics for 16,245 children in a prescription database. Ten per cent of the prescriptions were followed by a new prescription within 10 days. In children who received two prescriptions (n = 3993), 19% redeemed the prescriptions within the same course. When the child was prescribed penicillin V, compared with broad-spectrum penicillin, the odds ratio of receiving a repeat prescription within 1-2 days was 2.9 (95% CI 2.5-3.4) and within 3-10 days 1.3 (95% CI 1.2-1.5).

Superbugs: How They Evolve and Minimize the Cost of Resistance

The increasing frequency with which antimicrobial-resistant microorganisms have emerged in hospitals and communities has alarmed public health officials worldwide. The emergence of resistance results from the evolution of the sometimes elegant resistance mechanisms that create so-called superbugs, which disseminate by clonal spread or exchange resistance traits with other microorganisms. One major contributor to the emergence of resistance is selection intensity, which is determined by the volume of drug consumption by humans and the agriculture industry. De novo or acquired resistance is often initially associated with a cost to fitness of the microorganism. It therefore seems reasonable to assume that reducing the volume of drug use would slow the evolution and reduce the prevalence of resistance. This assumption has led to worldwide attempts to control the inappropriate use of antimicrobials in the hope of controlling the pandemic of antibiotic resistance. However, microorganisms have learned to adapt in order to survive in ever-changing environments. Superbugs have evolved numerous mechanisms that reduce or eliminate the cost of resistance, and such adaptations may minimize the potential benefits of programs aimed at reducing the volume of drug use. It therefore behooves us to look to other disciplines--such as population genetics, ecology, and mathematical biology--to help us tackle this perplexing and important problem.

Ribosomal Resistance: Emerging Problems and Potential Solutions

Many systemic antibiotics use ribosomal inhibition to suppress the replication of bacteria. Current research suggests that resistance to macrolide, lincosamide, and streptogramin B (MLS(B)) antibiotics is emerging among clinical isolates of Streptococcus pyogenes and Streptococcus pneumoniae. Erythromycin methylases, encoded by erm genes, modify an essential adenine residue in 23S rRNA and confer cross-resistance to MLS(B) antibiotics. More recently, macrolide efflux (mef) genes were identified in isolates of S. pyogenes and S. pneumoniae that show resistance to 14- and 15-membered macrolides (M phenotype). Resistance to MLSB has been associated with the increased use of erythromycin, and the recent emergence of the M phenotype has coincided with the marketing of newer macrolides. However, despite increasing macrolide resistance among clinical isolates of S. pneumoniae, convincing data on treatment failures directly attributable to MLS(B) or M phenotypes are limited. Possible solutions to emerging MLS(B) and M phenotype resistance include the introduction of alternative antibiotics, the more prudent use of antibiotics, combination therapy, molecular diagnostics, enhanced understanding of pharmacodynamic variables, and redefined resistance breakpoints.

Antibiotic policies in Central/Eastern Europe (CEE) after 1990

Significant political and social changes in Eastern Europe have caused dramatic changes in healthcare: Centralized state drug policies were decentralized, vaccination strategies in some countries changed and directed financing of healthcare replaced by one or multiple health management organisations (HMO). Centralized Infectious Diseases and/or Antibiotic Resistance surveillance were stopped after 1990 in four of six countries but resurrected after 1996 in Hungary, Poland and Slovakia. According to antibiotic (ATB) resistance and nosocomial infection rates, there are some differences in comparison to Western and Northern Europe e.g., a higher incidence of penicillin resistant pneumococci, ampicillin resistant H. influenzae and methicillin resistant Staphylococcus aureus. Because of increasing consumption of ATB before 1991, due to the free market, pharmaceutical marketing and reimbursement policies, several strategies to decrease consumption and/or resistance were implemented such as restriction of outpatient use, national and hospital formularies and Health Management Organizations-based restrictions. Probably due to the short time scale, no significant reduction in resistance has been documented although antibiotic consumption has declined.

Public beliefs and use of antibiotics for acute respiratory illness

OBJECTIVE

To better understand public beliefs and use of antibiotics for acute respiratory illnesses.

DESIGN

Cross-sectional telephone survey.

PARTICIPANTS

Three hundred eighty-six adult members (aged 18 years or older) of a group-model HMO in the Denver metropolitan area.

MEASUREMENTS AND MAIN RESULTS

Two hundred seventy-three (70%) of the respondents reported that antibiotics were beneficial for bacterial respiratory illnesses, 211 (55%) reported that antibiotics were beneficial for viral respiratory illnesses, and 82 (21%) reported that antibiotics were beneficial for bacterial but not for viral illness. Multivariate regression analysis identified consulting an advice nurse (odds ratio [OR] 2.9; 95% confidence interval [CI] 1.7, 5.3), ever being told by a provider that antibiotics were not needed for a respiratory illness episode (OR 2.0; 95% CI 1.2, 3.6), having a chronic medical condition (OR 2.0; 95% CI 1.0, 3.9), and believing antibiotics to be helpful for viral (OR 2.5; 95% CI 1.3, 4.7) or bacterial (OR 2.6; 95% CI 1.2, 6.7) respiratory illnesses to be independently associated with antibiotic use for respiratory illnesses during the previous year. There was a trend toward lower previous antibiotic use among those believing antibiotics to be helpful for bacterial illness but not for viral illness.

CONCLUSIONS

A lack of understanding about antibiotic effectiveness exists in the community. Increased previous antibiotic use among those believing antibiotics to be effective for viral illnesses suggests that improvements are needed in communications to patients and the public about antibiotic appropriateness.

Is there an ecological relationship between rates of antibiotic resistance of species of the genus Streptococcus? The Spanish Surveillance Group for Respiratory Pathogens

The relationship between resistance to antibiotics on the part of Streptococcus pneumoniae and Streptococcus pyogenes was studied by comparing different prevalences of resistance among hospitals obtained from a recent microbiological surveillance of community-acquired respiratory tract infections. A high correlation for erythromycin resistance was found between S. pneumoniae isolates from lower respiratory tract infections and S. pyogenes isolates collected from pharyngeal swabs.

Antibiotic use in humans and bacterial resistance

As with any public health problem, the evolution of antibacterial resistance must be viewed from a perspective of risk, and analysed in terms of probabilities within the populations. It is necessary to be able to predict the risk of antibacterial resistance, in the future, and two main strategies have recently been developed in mathematical models that may help to evaluate these risks. It is also important to understand how antibiotics are used and how their use affects the evolution of antibacterial resistance. Understanding the epidemiology of antibacterial resistance will enable us to develop preventive strategies to limit existing resistance and to avoid the emergence of new strains of resistant bacteria.

Evaluation of clinical practice guidelines on outcome of infection in patients in the surgical intensive care unit

OBJECTIVE

In this study, clinical practice guidelines were developed by a multidisciplinary team for patients with infections admitted to a surgical intensive care unit (ICU).

DESIGN

A 51-day baseline audit period (Phase I) in a 20-bed (private rooms) surgical ICU was compared with a 34-day period in the same unit after implementation of the guidelines (Phase II).

PATIENTS

Phase I included 182 patients (670 patient days), and Phase II included 139 patients (427 patient days).

RESULTS

There was no significant difference between patients in the Phase I and Phase II groups regarding age (65.4/19-95 vs. 64.8/18-90 yrs), gender (56% male vs. 55% male), severity of illness (mean Acute Physiology and Chronic Health Evaluation III, 38 vs. 39.1), total infections (respiratory, 8% vs. 4%; urinary tract, 15% vs. 4%; wound, 4% vs. 3%; skin/soft tissue, 3% vs. 7%; sepsis, 5% vs. 3%; intra-abdominal, 9% vs. 17%), and no infection (64% vs. 67%). Clinical outcomes of patients with infections in the Phase I group compared with those in the Phase II group were as follows: clinical improvement or cure, 64% vs. 76%; persistent infection, 17% vs. 11%; clinical failure, 0 vs. 2%; and death, 18% vs. 7% (p = NS). When patients with infections were compared, death rates were 20% in the Phase I group and 5.6% in the Phase II group (p = .02). After implementation of the clinical pathways, antibiotic costs were reduced from $676.54 per patient to $157.88 per patient (p = .001). Length of stay in the ICU was 3.7 days in the Phase I trial and a mean of 3 days in the Phase II trial (p = NS). Specimens of Escherichia coli demonstrated a trend toward a decreased resistance to all antibiotics and Pseudomonas aeruginosa to ciprofloxacin and aminoglycosides (p = NS).

CONCLUSIONS

In this study, the use of clinical practice guidelines for patients who were admitted to the surgical ICU was shown to reduce costs, without adversely affecting patients' outcomes. This study has important implications for the use of clinical practice guidelines for the management of patients with infections who are admitted to surgical ICUs.

Role of Antimicrobial Stewardship in Prevention and Control of Antibiotic Resistance

Evidence linking antimicrobial use with resistance is compelling on the local, national, and international levels. That resistance levels can be influenced by changing patterns of use also seems clear. We must now determine how, as a global society, to best use the resource of antimicrobials and how to protect novel compounds that are just now becoming available from emerging resistance. We must act not only within the arena of human use but also on use in animals and for crops.

Prevalence of mefE, erm and tet(M) genes in Streptococcus pneumoniae strains from Central Italy

One hundred and seventy-three Streptococcus pneumoniae strains isolated from surveillance studies conducted in daycare centres were studied. The mefE, erm and tet(M) genes were detected in 16.2, 45.1 and 47.4% of isolates respectively. Agreement between PCR results and antibiotic susceptibility patterns was 100%. Macrolide resistance was due to the presence of erm in 73.6% of strains and to the presence of mefE in the remaining 26.4%. All tetracycline resistant strains carried the tet(M) gene. erm was associated with tet(M) in 98.7% of strains, whereas no isolate carrying mefE carried tet(M). A significant association was found between mefE and serogroup 6 (P < 0.0005) and between erm and tet(M) and serogroup 19 (P < 0.00001).

Prevalence and mechanisms of macrolide resistance in clinical isolates of group A streptococci from Ontario, Canada

A total of 3,205 group A streptoccal isolates were collected in 1997 through a private laboratory which serves community physicians in southern Ontario and which represents a population base of 6 million people. Nonsusceptibility to erythromycin was detected for 67 (2.1%) isolates both by disk diffusion and by broth microdilution. Of these, 47 (70%) were susceptible to clindamycin and were found by PCR to possess the mef gene. Of the other 20 strains, 18 and 2 showed inducible and constitutive resistance, respectively, to clindamycin. Nineteen of these strains were shown by PCR to possess the ermTR gene, and a single constitutively resistant strain harbored an ermB gene. Sixteen (24%) erythromycin-resistant strains were also resistant to tetracycline. All were susceptible to penicillin and chloramphenicol.

Correlation between consumption of antimicrobials in humans and development of resistance in bacteria

The correlation between consumption of antimicrobials in humans and the emergence of resistance in bacteria is complex and has proved difficult to establish. Besides antimicrobial use, many other distinct contributing factors are also involved in the issue. Despite this complexity, there is a substantial body of evidence that the use of antibiotics in prophylaxis and in therapy is associated with the development of resistance in the hospital and in the community. Some examples are reviewed, including increase of resistance in enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter spp., Streptococcus pneumoniae, Staphylococcus aureus, Coagulase Negative Staphylococci and Streptococcus pyogenes after the use of beta-lactam antibiotics, aminoglycosides, fluoroquinolones and macrolides. Success in reversing the rise of resistant strains has been rarely described. Two examples are highlighted, the reduction in the incidence of nasal carriage of penicillin-resistant pneumococci in Icelandic children, and a significant decline in erythromycin resistance in S. pyogenes after the reduction in the use of macrolides in Finland.

Surveillance of antibiotic resistance

Resistance among bacteria is on the rise, both in the hospital and in the community. Surveillance is needed for guided empiric treatment and to detect new resistance mechanisms at an early stage. Surveillance shows a wide variation in resistance among hospitals and countries. Especially methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci are uncommon in north western European countries but frequently observed otherwise elsewhere. Among Gram-negative bacteria regional differences are less obvious. Many hospitals all over the world suffer from recurrent outbreaks by Enterobacteriaceae that produce extended spectrum beta-lactamases, Acinetobacter, etc. Because of the evolving pattern of resistance, surveillance should be done at regular intervals in all hospitals and in the community.

Self-medication of antibacterials without prescription (also called 'over-the-counter' use). A report of a Working Party of the British Society for Antimicrobial Chemotherapy

The availability of antimicrobial agents for self-medication may increase and could include antibacterial agents for oral or topical use. Wholesale deregulation of antibacterials would be undesirable and likely to encourage misuse of classes of agents currently important in the management of serious infections. Changed regulation from Prescription-Only Medicine (POM) to Pharmacy (P) medicine of selected agents with indications for short-term use in specific minor infections and illness is likely to have advantages to the user. However, safeguards to their use would need to be included in the Patient Information Leaflet (PIL). Agents and indications for self-medication are discussed. Any alteration in licensed status from POM to P will require careful risk-benefit assessment, including the likely impact on bacterial resistance. Safety issues also include concerns relating to age of the user, pregnancy, underlying disease and the potential for drug interactions. The importance of appropriate information with the PIL is emphasized, as is the role of the pharmacist, while ways of improving adverse event notification and monitoring are discussed. The paucity of good denominator-controlled data on the prevalence of in-vitro resistance is highlighted, and recommendations for improving the situation are made. There are currently no levels of resistance accepted by regulatory bodies on which to base a licensing decision, be it for granting a product licence, renewal of a licence or a change in licensed status from POM to P. Due consideration should be given to: the validation of user-defined indications in comparison with those medically defined; the enhancement of pharmacy advice in the purchase of such agents; improved safety monitoring; the establishment of systematic surveillance of susceptibility data.

Association between the consumption of antimicrobial agents in animal husbandry and the occurrence of resistant bacteria among food animals

Antimicrobial agents are used in food animals for therapy and prophylaxis of bacterial infections and in feed to promote growth. The use of antimicrobial agents for food animals may cause problems in the therapy of infections by selecting for resistance among bacteria pathogenic for animals or humans. The emergence of resistant bacteria and resistance genes following the use of antimicrobial agents is relatively well documented and it seems evident that all antimicrobial agents will select for resistance. However, current knowledge regarding the occurrence of antimicrobial resistance in food animals, the quantitative impact of the use of different antimicrobial agents on selection for resistance and the most appropriate treatment regimens to limit the development of resistance is incomplete. Surveillance programmes monitoring the occurrence and development of resistance and consumption of antimicrobial agents are urgently needed, as is research into the most appropriate ways to use antimicrobial agents in veterinary medicine to limit the emergence and spread of antimicrobial resistance.

Susceptibility of group A beta-hemolytic streptococci in the lower St Lawrence region, Quebec

OBJECTIVE

To determine the susceptibility of group A beta-hemolytic streptococci (GABHS) in the lower St Lawrence region, Quebec to different antibiotics, particularly macrolides, and to compare different antibiogram methods (disk diffusion, E-test and microdilution) and incubation atmospheres (ambient air and 5% carbon dioxide).

METHODS

A total of 384 strains of GABHS isolated from 377 patients (throat 335; other sites 49) from three hospitals in the lower St Lawrence region were analyzed for their susceptibility to erythromycin, clarithromycin, azithromycin, penicillin, clindamycin, cephalothin, rifampin and vancomycin by disk diffusion on Mueller-Hinton (MH) agar supplemented with 5% defibrinated sheep blood (MHB) at 35ºC in 5% carbon dioxide. Strains that were found to be intermediately resistant or resistant to one of the antibiotics by disc diffusion, strains from sites other than throat, and a sample of 97 pharyngeal strains were evaluated by E-test on MHB (35ºC, 5% carbon dioxide) for their susceptibility to the antibiotics erythromycin, clarithromycin, azithromycin, penicillin, clindamycin and ceftriaxone. In addition, minimum inhibitory concentrations (MICs) were determined for erythromycin and azithromycin by broth microdilution using MH broth supplemented with 2.5 % of lysed horse blood (35ºC, ambient air) on strains that were resistant or intermediately resistant to the macrolides (erythromycin, clarithromycin, azithromycin). An evaluation was also carried out on these strains to determine the influence of the incubating atmosphere (ambient air versus 5% carbon dioxide) on susceptibility results obtained by disk diffusion (erythromycin, clarithromycin and azithromycin) and E-test (erythromycin and azithromycin) methods.

RESULTS

Nine strains (2%) from nine patients (throat eight, pus one) were resistant to all macrolides as tested by three different techniques (disk diffusion, E-test and microdilution). All strains were susceptible to all the other antibiotics tested. For the strains intermediately resistant or resistant to macrolides, incubation in a 5% carbon dioxide atmosphere was associated with a reduction in the diameter of inhibition determined by disk diffusion (P<0.001) with frequent minor variations in interpretation, and with an increase in the MIC by E-test (P<0.001), which had no impact on interpretation.

CONCLUSIONS

Resistance of GABHS to macrolides was not common (2%) in the lower St Lawrence Region. GABHS susceptibility to erythromycin seemed to predict the susceptibility to the other macrolides. Significant variation in antibiogram results (disk diffusion and E-test) of GABHS susceptibility to macrolides was related to the incubation atmosphere and may have an impact on the interpretation of disk diffusion results.

Pneumococcal macrolide resistance--myth or reality?

There is no doubt that owing to the prolific use of the macrolides and azithromycin over the past several years, resistance has developed and is increasing in incidence. I believe we should re-evaluate the use of these antibiotics for our patients and consider parameters other than the negative in-vitro results. Firstly, microbiology laboratories should return to the habit of providing the clinician with MIC values for pathogenic isolates rather than generic susceptibility reports ((S)usceptible, (I)ntermediate, (R)esistant) that are based on standard disc diffusion testing. Although agar dilution MIC testing is a bulky and labour intensive practice, it provides the best data when conducted in the appropriate environment. Secondly, and more importantly, these MIC values need to be compared with in-vivo antibiotic pharmacokinetics and pharmacodynamics. Although it is possible to compare MIC values directly with serum concentrations of beta-lactams and aminoglycosides, this is not a valid practice for azithromycin or the macrolides. MICs of azithromycin and the macrolides must be compared with the infection site and phagocytic cell concentrations to determine the utility, or lack thereof, of one of these agents. Whereas azithromycin cellular penetration allows maximal pharmacodynamics potentially even against moderately or highly resistant pneumococci, the macrolides do so less optimally. Although there are no reports of widespread clinical failures resulting from macrolide/azalide resistance in pneumococci, it is expected that such reports will appear once the isolates become consistently highly resistant. This is likely to affect the macrolides, erythromycin and clarithromycin, before the azalide, azithromycin owing to the differences in pharmacokinetics of these drugs. Until then, it will be important to determine the MICs of not just one macrolide, but of all macrolides and azalides for the isolates. This will allow the clinician to make a pharmacokinetically and pharmacodynamically sound choice. By choosing clinical MIC breakpoints of 4-8 mg/L for oral macrolides and < or = 32 mg/L for oral azithromycin, rather than the present standard breakpoints, the clinician can make a macrolide/azalide choice that will optimize the pharmacodynamics of the drug against the isolated pathogen and result in the best possible clinical outcome. Once data concerning the cellular penetration of intravenous formulations of these drugs becomes available, it will be possible to develop clinical breakpoints for these formulations as well. Only through utilizing good antibiotic prescribing practices and by using the drugs appropriately when they are used, can resistance trends be stemmed. In this way, not only does a clinician treat the patient more effectively, but they also extend the antibiotic's useful life.

Antibiotics in acute bronchitis: a meta-analysis

PURPOSE

Most patients with acute bronchitis who seek medical care are treated with antibiotics, although the effectiveness of this intervention is uncertain. We performed a meta-analysis of randomized, controlled trials to estimate the effectiveness of antibiotics in the treatment of acute bronchitis.

SUBJECTS AND METHODS

English-language studies published January 1966 to April 1998 were retrieved using MEDLINE, bibliographies, and consultation with experts. Only randomized trials that enrolled otherwise healthy patients with a diagnosis of acute bronchitis, used an antibiotic in the treatment group and a placebo in the control group, and provided sufficient data to calculate an effect size were included.

RESULTS

We identified eight randomized controlled trials that satisfied all inclusion criteria. These studies used one of three antibiotics (erythromycin, doxycycline, trimethoprim/sulfamethoxazole). The use of antibiotics decreased the duration of cough and sputum production by approximately one-half day (summary effect size 0.21; 95% CI, 0.05 to 0.36). For specific symptoms, there were nonsignificant trends favoring the use of antibiotics: a decrease of 0.4 days of purulent sputum (95% CI, -0.1 to 0.8), a decrease of 0.5 days of cough (95% CI, -0.1 to 1.1), and a decrease of 0.3 days lost from work (95% CI, -0.6 to 1.1).

CONCLUSION

This meta-analysis suggests a small benefit from the use of the antibiotics erythromycin, doxycycline, or trimethoprim/sulfamethoxazole in the treatment of acute bronchitis in otherwise healthy patients. As this small benefit must be weighed against the risk of side effects and the societal cost of increasing antibiotic resistance, we believe that the use of antibiotics is not justified in these patients.

Antimicrobial resistance in intensive care units

The unique nature of the intensive care unit (ICU) environment makes this part of the hospital a focus for the emergence and spread of many antimicrobial-resistant pathogens. There are ample opportunities for the cross-transmission of resistant bacteria from patient to patient, and patients are commonly exposed to broad-spectrum antimicrobial agents. Rates of resistance have increased for most pathogens associated with nosocomial infections among ICU patients, and rates are almost universally higher among ICU patients compared with non-ICU patients. There are many opportunities, however, to prevent the emergence and spread of these resistant pathogens through improved use of established infection control measures (i.e., patient isolation, hand washing, glove use, and appropriate gown use), and implementation of a systematic review of antimicrobial use.

Causes, diagnosis and treatment of pharyngitis

Pharyngitis is the only respiratory tract infection in which microbiologic diagnosis has immediate influence on the treatment decision. Microbiologic diagnosis should always precede antibiotic treatment of pharyngitis to ensure optimal treatment. Penicillin administered for 10 days is still the drug of choice.

Detection of antimicrobial activity in urine for epidemiologic studies of antibiotic use

Antibiotic resistance is the inevitable consequence of the selective pressure of antimicrobial drug use and the adaptive plasticity of the microorganisms. Excessive and irrational use of antimicrobial drugs is a problem in all countries. It is particularly troublesome in developing countries where there is a heavy burden of infectious diseases. This study was designed to determine whether detection of antimicrobial activity in the urine might be a useful tool for epidemiologic studies of the interaction between antibiotic use and resistance in developing countries. A laboratory marker is necessary because the history of antimicrobial drug use may be unreliable. Serial specimens or spontaneously voided urine were obtained from healthy volunteers given a single oral dose of commonly used antimicrobial drugs. Urine was also obtained from hospitalized patients the morning after the last dose of an antimicrobial drug and from untreated controls. Assays were performed with standard American Type Culture Collection (Rockville, MD) stains of Bacillus stearothermophilus, Escherichia coli, and Streptococcus pyogenes. Antimicrobial activity could not be detected in pretreatment urine. After a single oral dose, the beta lactam antibiotics and erythromycin could be detected for about 12 to 24 hours, whereas clindamycin, tetracycline, trimethoprim/sulfamethoxazole, and ciprofloxacin could be detected for 48 or more hours. In hospitalized patients, receiving multiple drugs, the following were the sensitivity and specificity for detection of antimicrobial activity: for B. stearothermophilus, 100.0% and 85.9%, respectively; for S. pyogenes, 94.9% and 94.9%, respectively; and for E. coli, 71.8% and 98.7%, respectively. The combination of E. coli and Streptococcus pyogenes exhibited a sensitivity of 97.4% and specificity of 94.9%. Detection of antimicrobial activity in urine is a promising method to determine antimicrobial drug use in epidemiologic studies, particularly in populations in which drug use history is unreliable.

Characterization of antimicrobial resistance in Streptococcus pyogenes isolates from the San Francisco Bay area of northern California

During 1994 and 1995, 157 isolates of Streptococcus pyogenes from patients with invasive disease were consecutively collected in the San Francisco Bay area to determine the frequency of antimicrobial resistance. Susceptibility testing was performed according to the guidelines of the National Committee for Clinical Laboratory Standards by the disk method and by broth microdilution. For comparison of susceptibility patterns, an additional 149 strains were randomly collected from patients with pharyngitis. For San Francisco County, 32% of the isolates from invasive-disease-related specimens but only 9% of the isolates from throat cultures from the same period were resistant to erythromycin (P = 0.0007). Alameda County and Contra Costa County had rates of resistance of </=10% from isolates from all cultures. When the data were analyzed by hospital, the San Francisco County Hospital had a statistically higher rate of erythromycin resistance (39%) among the strains from serious infections compared to those from other counties (P = <0. 0003). For tetracycline, high rates of resistance were observed in San Francisco County for both isolates from patients with invasive disease (34%) and pharyngitis (21%) in the same period. Using pulsed-field gel electrophoresis, two clones, one at the San Francisco County Hospital and a second in the entire area, were identified. The latter clone exhibited resistance to bacitracin. Of 146 strains that were tested by microdilution, all were susceptible to penicillin. Clindamycin resistance was not seen among the erythromycin-susceptible strains, but two of the 39 erythromycin-resistant strains were also resistant to clindamycin. An additional 34 strains showed resistance to clindamycin when exposed to an erythromycin disk in the double-disk diffusion test, suggesting that the mechanism of erythromycin resistance is due to an erm gene. This study demonstrates a high rate of resistance to macrolides and tetracycline among S. pyogenes isolates in San Francisco County and shows that macrolide resistance is more common in strains from patients with invasive disease than in strains from those with pharyngitis.

Studies of antibiotic resistance within the patient, hospitals and the community using simple mathematical models

The emergence of antibiotic resistance in a wide variety of important pathogens of humans presents a worldwide threat to public health. This paper describes recent work on the use of mathematical models of the emergence and spread of resistance bacteria, on scales ranging from within the patient, in hospitals and within communities of people. Model development starts within the treated patient, and pharmacokinetic and pharmacodynamic principles are melded within a framework that mirrors the interaction between bacterial population growth, drug treatment and the immunological responses targeted at the pathogen. The model helps identify areas in which more precise information is needed, particularly in the context of how drugs influence pathogen birth and death rates (pharmacodynamics). The next area addressed is the spread of multiply drug-resistant bacteria in hospital settings. Models of the transmission dynamics of the pathogen provide a framework for assessing the relative merits of different forms of intervention, and provide criteria for control or eradication. The model is applied to the spread of vancomycin-resistant enterococci in an intensive care setting. This model framework is generalized to consider the spread of resistant organisms between hospitals. The model framework allows for heterogeneity in hospital size and highlights the importance of large hospitals in the maintenance of resistant organisms within a defined country. The spread of methicillin resistant Staphylococcus aureus (MRSA) in England and Wales provides a template for model construction and analysis. The final section addresses the emergence and spread of resistant organisms in communities of people and the dependence on the intensity of selection as measured by the volume or rate of drug use. Model output is fitted to data for Finland and Iceland and conclusions drawn concerning the key factors determining the rate of spread and decay once drug pressure is relaxed.

A population-based study of antibiotic prescriptions for Danish children

BACKGROUND

The aim of the study was to examine the use of systemic and topical antibiotics in relation to age and sex in Danish children.

METHODS

We used the Pharmacoepidemiological Prescription Database to identify the individual prescriptions of antibiotics provided for all 0-to 15-year-old children in North Jutland County, Denmark, during 1997. The population was approximately 95000 children.

RESULTS

We identified 44640 prescriptions for systemic antibiotics. The annual prescription rate was highest in the 1- to 2-year-olds, with 945 prescriptions/1000 children/year. One-half of these children received at least 1 prescription, and 12% received 3 or more prescriptions. Among the 11- to 15-year-old children 17% received one or more prescriptions. Overall 88% of the prescriptions were penicillins and 10% were macrolides. In children younger than 3 years 57% of prescriptions were for broad spectrum penicillins, but in children older than 6 years penicillin V was the most frequently used antibiotic. We identified 12 661 prescriptions for topical antibiotics used in eye infections. The prescription rate peaked in the 1- to 2-year-old children, one-third of whom received at least 1 prescription.

CONCLUSIONS

Almost two-thirds of the 0- to 2-year-old children in the population were treated with either systemic or topical antibiotics during 1 year. Physicians prescribe mostly penicillins, but the proportion of broad spectrum penicillins for young children was so high, however, that enforcement of national guidelines should be reconsidered.

Survey of clinical pharmacists' knowledge of appropriateness of antimicrobial therapy for upper respiratory infections and acute bronchitis

We conducted a survey to assess clinical pharmacists' recommendation of antibiotics for upper respiratory infections (URIs) and acute bronchitis. A random sample of 752 members of the American College of Clinical Pharmacy were mailed a multiple-choice survey that presented four examples consistent with clinical symptoms of the two disorders. Respondents were asked what treatment they would recommend for each example. The response rate was 59%. Pharmacists recommended antibiotics for the treatment of both URIs and acute bronchitis significantly more if patients' symptoms included discolored discharge or sputum as opposed to clear discharge. Those who were board certified were less likely than nonboard-certified pharmacists to recommend antibiotics for URIs with discolored discharge. Pharmacists who specialized in either ambulatory care or infectious disease were less likely than those in other specialties to recommend antibiotics for acute bronchitis with discolored sputum. Clinical pharmacists are similar to patients and physicians in their belief that antibiotics are appropriate for URIs and acute bronchitis with discolored discharge. Considering the role that pharmacists play as clinical consultants to physicians, greater efforts should be made to educate them regarding appropriate prescription of antibiotics.

Incidence of erythromycin resistance in Streptococcus pyogenes: a 10-year study

We studied the evolution of susceptibility of Streptococcus pyogenes isolated in our hospital from 1987 to 1996. Susceptibility to penicillin, ampicillin, cefotaxime, cefuroxime, imipenem, erythromycin, clindamycin, tetracycline, vancomycin, ciprofloxacin, rifampin, and chloramphenicol was determined by the National Committee for Clinical Laboratory Standards broth microdilution method. Differentiation of phenotypes of erythromycin-resistant strains was performed using the double-disc method. All isolates remained very susceptible in vitro to penicillin and all of the other beta-lactam agents tested. Between 1987 and 1995 the incidence of erythromycin resistant strains remained below 5%; the difference in the resistance rate between 1995 (2.6%) and 1996 (17.1%) was statistically significant. The macrolide resistance M phenotype was the most frequent. The isolation rates of tetracycline-resistant strains increased from 2.2% in 1987 to 11.2% in 1988. The marked increase in the incidence of erythromycin resistance observed in our area warrants periodic surveillance of antibiotic susceptibility of S. pyogenes isolates and emphasizes the need to control outpatient antibiotics. The preponderance of the M phenotype may have implications in the choice of antibiotic.

A review of Chlamydia pneumoniae and atherosclerosis

Chlamydia pneumoniae is a Gram-negative obligate intracellular bacterium that causes acute upper and lower respiratory infections. Its distribution is worldwide. Seroepidemiological studies have shown an association between C. pneumoniae and atherosclerosis, and the risk of acute myocardial infarction. Several studies had detected C. pneumoniae in atherosclerotic lesions from coronary and carotid arteries, in abdominal aortic aneurysms (AAA), and in sclerotic aortic valves. One study consistently succeeded in culturing C. pneumoniae from an atherosclerotic lesion, indicating the presence of viable organisms. However, the pathogenicity is unknown, and the significance of detecting the organism is unresolved. In two minor controlled clinical trials, patients with ischaemic heart disease were randomised into antibiotic-treated and placebo groups. Both trials showed a significant reduction in serious endpoints in patients receiving macrolide. Macrolide therapy thus seems to improve the outcome of severe ischaemic heart disease. It is not known whether this is caused by eradicating C. pneumoniae organisms, or by the macrolide's non-specific anti-inflammatory effect. Since both C. pneumoniae and inflammation are found in the AAA wall, it may be considered that macrolide would also improve the outcome of AAA and other diseases related to vascular surgery. In order to confirm this, randomised trials with macrolide therapy are needed, as well as diagnostic methods that can differentiate between individuals who are or are not infected with C. pneumoniae. The latter are needed in order to clarify the impact of the presence of C. pneumoniae and to avoid indiscriminate use of antimicrobials.

Nosocomial pneumonia in the ICU--year 2000 and beyond

Diagnostic and treatment strategies in ICU patients with ventilator-associated pneumonia (VAP) remain controversial, largely because of the paucity of well-controlled comparison trials using clinically important end points. Recent studies indicating that early appropriate antibiotic therapy significantly lowers mortality underscore the urgent need for well-designed comparative trials. When quantitatively cultured, bronchial specimens obtained by noninvasive techniques may provide clinically useful information and avoid the higher costs and risks of invasive bronchoscopic diagnostic techniques. Previous antibiotic use before onset of nosocomial pneumonia raises the likelihood of infection with highly virulent organisms, such as Pseudomonas aeruginosa and Acinetobacter sp. Thus, the empiric antibiotic regimen should be active against these Gram-negative pathogens as well as other common Gram-negative and Gram-positive causative organisms. Promising preventive modalities for nosocomial VAP include use of a semirecumbent position, endotracheal tubes that allow continuous aspiration of secretions, and heat and moisture exchangers. Rotating their standard empiric antibiotic regimens and restricting the use of third-generation cephalosporins as empiric therapy may help hospitals reduce the incidence of nosocomial pneumonia caused by resistant Gram-negative pathogens.

A cross-Canada surveillance of antimicrobial resistance in respiratory tract pathogens

OBJECTIVE

To determine the prevalence of antimicrobial resistance in clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis from medical centres across Canada.

METHODS

Fifty laboratories from across Canada were asked to collect up to 25 consecutive clinical isolates of S pneumoniae, H influenzae and M catarrhalis at some time between September 1994 and May 1995, and then again between September and December of 1996. A total of 2364 S pneumoniae, 575 H influenzae and 200 M catarrhalis samples were collected. H influenzae and M catarrhalis isolates were tested for the production of beta-lactamase. S pneumoniae isolates were characterized as penicillin susceptible, intermediately resistant or high level penicillin-resistant. Minimal inhibitory concentrations (MICs) were determined using a microbroth dilution technique described by the National Committee of Clinical Laboratory Standards.

RESULTS

Between the two collection periods, there was a significant increase in highly penicillin-resistant S pneumoniae from 2.1% to 4.4% (P<0.05) and an increase in intermediately penicillin-resistant strains from 6.4% to 8.9% (P<0.05). A significant increase in high level penicillin-resistant S pneumoniae was noted among paediatric isolates. No significant difference in the susceptibilities of comparator agents was detected. A significant increase in the number of beta-lactamase producing H influenzae, 34% to 43% (P<0.05) was observed. Ninety-five per cent of M catarrhalis isolates were beta-lactamase producers in both time periods.

CONCLUSIONS

During the course of this study, the incidence of penicillin resistance in S pneumoniae doubled. As a result of this increase, infections due to this organism in sites where poor penetration of beta-lactam antibiotics occur may become increasingly difficult to manage.

Antibiotic prescribing for respiratory tract infections in general practice

OBJECTIVES

(1) To describe interpractice variation in diagnosis of respiratory infections at consultation. (2) To test the hypotheses that: (a) The decision to prescribe an antibiotic in respiratory infection is influenced by the diagnosis, the perceived certainty of diagnosis, and whether or not a consultation takes place. (b) The choice of antibiotic is influenced by the diagnosis.

DESIGN

A regional survey of prescribing and associated morbidity in general practice, over a 2-week period in April 1994.

SETTING

Stratified quota sample of 22 Northern Ireland practices.

RESULTS

There was wide interpractice variation in diagnosis of common respiratory infections at consultation, especially tonsillitis (5.0-157.5/1000 consultations). Overall, different diagnoses predicted the decision to prescribe an antibiotic at different levels (coryza 42.3%, tonsillitis 84.8%), but there was wide interpractice variation in the decision to prescribe for most diagnoses. With the exception of coryza and sinusitis, the perceived certainty of diagnosis did not significantly influence the decision to prescribe. The decision to prescribe was not significantly influenced by whether or not a consultation took place. Overall, broad spectrum penicillins were the therapeutic group most frequently prescribed for a given diagnosis with the exception of tonsillitis (phenoxymethylpenicillin) and sinusitis (tetracyclines), but there was wide interpractice variation in choice of antibiotic.

CONCLUSIONS

Little consensus exists among practices regarding rational prescribing decisions in respiratory illness. The absence of a consultation was no deterrent to antibiotic prescribing. At one extreme, it is suggested that some practices are avoiding consultations for respiratory infections. There is wide variation in choice of antibiotic, despite existing guidelines.

Population biology, evolution, and infectious disease: convergence and synthesis

Traditionally, the interest of population and evolutionary biologists in infectious diseases has been almost exclusively in their role as agents of natural selection in higher organisms. Recently, this interest has expanded to include the genetic structure and evolution of microparasite populations, the mechanisms of pathogenesis and the immune response, and the population biology, ecology, and evolutionary consequences of medical and public health interventions. This article describes recent work in these areas, emphasizing the ways in which quantitative, population-biological approaches have been contributing to the understanding of infectious disease and the design and evaluation of interventions for their treatment and prevention.