Bacteremic pneumonia due to Staphylococcus aureus: A comparison of disease caused by methicillin-resistant and methicillin-susceptible organisms

Therapy of ventilator-associated pneumonia. A patient-based approach based on the ten rules of "The Tarragona Strategy"

Therapy of ventilator-associated pneumonia should be a patient-based approach focusing on some key features are listed here: early initial therapy should be based on broad-spectrum antibiotics. Empirical treatment may be targeted after direct staining and should be modified according to good-quality quantitative microbiological findings, but should never be withdrawn in presence of negative direct staining or delayed until microbiological results are available. Courses of therapy should be given at high doses according to pharmacodynamic and tissue penetration properties. Prolonging antibiotic treatment does not prevent recurrences. Methicillin-sensitive Staphylococcus aureus should be expected in comatose patients. Methicillin-resistant Staphylococcus aureus should not be expected in patients without previous antibiotic coverage. Pseudomonas aeruginosa should be covered with combination therapy. Antifungal therapy, even when Candida spp is isolated in significant concentrations, is not recommended for intubated nonneutropenic patients. Vancomycin, given at the standard doses and route of administration for the treatment of VAP caused by Gram-positive pathogens, is associated with poor outcomes. The choice of initial antibiotic should be based on the patient's previous antibiotic exposure and comorbidities, and local antibiotic susceptibility patterns, which should be updated regularly.

Staphylococcus aureus bacteremic pneumonia: differences between community and nosocomial acquisition

OBJECTIVE

The aim of the study was to ascertain the clinical and epidemiologic characteristics of patients with nosocomial or community-acquired Staphylococcus aureus bacteremic pneumonia.

METHODS

A prospective study of 134 cases diagnosed between January 1990 and December 1995 was performed.

RESULTS

Fifty cases involved primary bacteremic pneumonias, of which 80% were nosocomial (the majority, 72%, in intensive care unit patients, of whom 57% were post-surgery). Of the 84 cases of secondary pneumonia, 36 were non-intravenous drug users (78% nosocomial, of whom 43% were in the intensive care unit), and 48 cases were intravenous drug users (98% community-acquired).

CONCLUSIONS

Nosocomial S. aureus bacteremic pneumonia was especially frequent in intensive care unit patients (68.1%), and community-acquired pneumonia in intravenous drug users (72.3%). In non-intravenous drug users, clinical outcome and mortality were similar for nosocomial and community-acquired pneumonia.

The influence of inadequate empirical antimicrobial treatment on patients with bloodstream infections in an intensive care unit

OBJECTIVE

To determine the occurrence of inadequate antimicrobial therapy among critically ill patients with bacteremia and the factors associated with it, to identify the microorganisms that received inadequate antimicrobial treatment, and to determine the relationship between inadequate treatment and patients outcome.

METHODS

From June 1995 to January 1999 we collected data on all clinically significant ICU-bacteremias in our teaching hospital. Clinical and microbiological characteristics were recorded and the adequacy of empirical antimicrobial treatment in each case was determined. We defined inappropriate empirical antimicrobial treatment as applying to infection that was not being effectively treated at the time the causative microorganism and its antibiotic susceptibility were known. Multivariate analysis was used to determine the variables associated with inappropriate empirical antimicrobial treatment and to evaluate the influence of this on the related mortality to bacteremia, using the SPSS package (9.0).

RESULTS

Among 166 intensive care unit patients with bacteremia, 39 (23.5%) received inadequate antimicrobial treatment. In this last group the mean age of patients was 64.1 +/- 13.2 years, and 64% were men. Bacteremia was hospital-acquired in 92% of these cases. Eleven percent developed septic shock and 37.7% severe sepsis, and ultimately fatal underlying disease was present in 28.2% of patients given inadequate empirical antimicrobial treatment. The main sources of bacteremias in this group were: a vascular catheter (15.3%), respiratory (7.6%) or unknown (53.8%). The microorganisms most frequently isolated in the group with inadequate empirical antimicrobial treatment were: coagulase-negative staphylococci (29.5%), Acinetobacter baumannii (27.3%), Enterococcus faecalis, Pseudomonas aeruginosa, Enterobacter cloacae, Proteus mirabilis, Escherichia coli, and Candida species (4.5% each). The frequency of coagulase-negative staphylococci in the cases with inappropriate treatment was higher than in the group with appropriate treatment (OR 2.62; 95% CI: 1.10-6.21; P = 0.015). The global mortality rate was 56% and the related mortality was 30% in the group with inadequate empirical antimicrobial treatment. The only factor associated with inappropriate empirical antibiotic treatment was the absence of abdominal or respiratory focus (P = 0.04; OR = 0.35; 95% CI: 0.12-0.97). Septic shock was related to attributable mortality (P = 0.03; OR = 3.19; 95% CI: 1.08-9.40), but not inappropriate empirical antibiotic treatment (P = 0.24; OR = 1.71; 95% CI: 0.66-4.78).

CONCLUSION

Almost a quarter of critically ill patients with bloodstream infections were given inadequate empirical antibiotic treatment, but mortality was not higher in the group with inadequate treatment than in the group with adequate treatment. This fact was probably due to microbiological factors and clinical features, such as the type of microorganism most frequently isolated and the source of the bacteremia.

[Respiratory infections in adults hospitalized in internal medicine and pneumology departments. DIRA (Adult Respiratory Infection Day) study]

INTRODUCTION

Respiratory tract infections (RIs) are frequent processes that can require hospitalization or affect already hospitalized patients. The Foundation for the Study of Infection has promoted the DIRA (Adult Respiratory Infection Day) Project, with the aim of investigating and assessing the impact of this problem, particularly in Internal Medicine and Pneumology Departments.

METHODS

Prospective prevalence study involving 158 physicians in 100 Internal Medicine and Pneumology Departments. Data were collected on predetermined days, once every three months (total of four data sets) and included information on number of patients attended, number of patients with infection, and epidemiologic, clinical, microbiologic and treatment characteristics of patients with RI.

RESULTS

A total of 3,596 patients were hospitalized at the four time points. Among these, 39.1% presented clinical symptoms consistent with infection and 34.3% of these were RIs. The mean age of RI patients was 65.6 years, 68.8% were males, 84.1% had an underlying disease (most frequently chronic obstructive pulmonary disease) and 25.1% had one or more predisposing factors. Pneumonia was the most frequent diagnosis (41.3% of RIs). RI was documented microbiologically in 15.8% of cases. Antibiotic treatment was applied in 99.7% of patients with acute bronchitis and 81.8% of those with upper respiratory tract infection; penicillins were the most frequent treatment. Data are presented by diagnosis.

CONCLUSIONS

A substantial rate of respiratory infections was found in patients admitted to hospital Internal Medicine and Pneumology Departments, with pneumonia being the most frequent. There was a paucity of microbiologic documentation. It is likely that antibiotic treatment was not justified in the majority of patients with upper respiratory tract infections. A combination of two or more antimicrobial agents was used in about half of cases.

Adverse clinical and economic outcomes attributable to methicillin resistance among patients with Staphylococcus aureus surgical site infection

Data for 479 patients were analyzed to assess the impact of methicillin resistance on the outcomes of patients with Staphylococcus aureus surgical site infections (SSIs). Patients infected with methicillin-resistant S. aureus (MRSA) had a greater 90-day mortality rate than did patients infected with methicillin-susceptible S. aureus (MSSA; adjusted odds ratio, 3.4; 95% confidence interval, 1.5-7.2). Patients infected with MRSA had a greater duration of hospitalization after infection (median additional days, 5; P<.001), although this was not significant on multivariate analysis (P=.11). Median hospital charges were 29,455 dollars for control subjects, 52,791 dollars for patients with MSSA SSI, and 92,363 dollars for patients with MRSA SSI (P<.001 for all group comparisons). Patients with MRSA SSI had a 1.19-fold increase in hospital charges (P=.03) and had mean attributable excess charges of 13,901 dollars per SSI compared with patients who had MSSA SSIs. Methicillin resistance is independently associated with increased mortality and hospital charges among patients with S. aureus SSI.

Importance of focus identification in the treatment of Staphylococcus aureus bacteraemia

Staphylococcus aureus bacteraemia increases in frequency, and it is still a life-threatening disease. In recent years, some interesting studies such as the need for focus identification and the focus eradication have been performed. The aim of this review is to present an up-to-date assessment of the current challenges in the management of S. aureus bacteraemia in order to improve the outcome.

Antimicrobial resistance in the intensive care unit: understanding the problem

Antimicrobial resistance is a problem that affects healthcare delivery around the globe. Factors associated with antimicrobial resistance include overuse or misuse of antimicrobial agents, immunosuppressed patients, and increased technology. Cellular mechanisms of antimicrobial resistance include the decreased uptake of a drug, efflux of the drug, enzymatic inactivation, and alterations in the antimicrobial target site. New treatment options are currently available for resistant organisms. Therapeutic strategies such as antibiotic control policies and antibiotic "cycling" have been proposed as methods for minimizing the emergence of more resistant organisms. Little evidence is available to indicate that these strategies are effective in limiting the emergence of resistance. Clinicians are urged to be judicious in their use and choice of antimicrobials.

Enterocolitis caused by methicillin-resistant Staphylococcus aureus: molecular characterization of respiratory and digestive tract isolates

We investigated the mechanism of outbreak of enterocolitis caused by methicillin-resistant Staphylococcus aureus (MRSA). Five epidemiological markers [coagulase type, enterotoxin type, toxic shock syndrome toxin-1 (TSST-1) production, beta-lactamase production and pulsed-field gel electrophoresis (PFGE)] of 45 strains of MRSA isolated simultaneously from the respiratory tract (nasal cavity and/or pharynx and/or sputum) and stool (plus one sample of gastric juice) in 13 patients (8 males and 5 females, mean age, 77.1 years) were compared retrospectively. Forty-four of the 45 isolates of MRSA were positive for enterotoxin C and TSST-1 production, and the remaining isolate was positive for enterotoxin A and negative for TSST-1 production. All isolates were coagulase type II, and 27 showed beta-lactamase production. The patterns of coagulase type, enterotoxin type, TSST-1 and beta-lactamase production of MRSA isolated from the respiratory tract were similar to those of MRSA isolated from the intestine in 12 of 13 patients. Molecular typing by PFGE demonstrated that the pattern of respiratory tract isolates was identical to those of stool isolates in 9 (69.2%), similar in 3 (23.1 %), and different in 1 (7.7%). The data suggested that enterocolitis might be caused by the MRSA colonized in the respiratory tract and incorporated into the digestive tracts. Therefore, we propose that early eradication of MRSA in the respiratory tract is important for protection of patients against the development of enterocolitis, particularly in susceptible patients, e.g., immunocompromised or pre-operated patients with digestive diseases, especially malignant disease.

Inadequate therapy and antibiotic resistance. Risk factors for mortality in the intensive care unit

BACKGROUND

The impact of nosocomial infections and multidrug resistance on mortality is a topic of considerable controversy.

METHODS

A prospective, nested case control study was conducted in four intensive care units (ICUs) in Mexico to measure the impact of antibiotic resistance on and identify the main risk factors for mortality in critically ill patients with nosocomial infections.

RESULTS

One hundred thirteen patients developed 119 nosocomial infections. Multivariate analysis identified two variables that were significantly and independently associated with mortality: ventilator-associated pneumonia (p = 0.0041, odds ratio [OR] = 7.7) and inadequate antibiotic treatment (p <0.0001, OR = 70.5). Although antibiotic resistance in Gram-negative rods was not an independent risk factor for mortality, there was a strong association between antibiotic resistance and inadequate treatment (chi2 for linear trend = 29.3, p <0.00001). For patients with ventilator-associated pneumonia, predicted mortality calculated by APACHE II score was 23% compared to an observed mortality of 71%.

CONCLUSIONS

In this study the major risk factors for mortality were inadequate antibiotic treatment and development of ventilator-associated pneumonia. Multidrug resistance significantly increased the probability of receiving inadequate antibiotic treatment. The striking differences between observed and predicted mortality in these four ICUs indicate the need for further research and a reassessment of the current programs for prevention and control of nosocomial infections in Mexico.

Staphylococcus aureus infections and antibiotic resistance in older adults

The prevalence of infection with Staphylococcus aureus among older adults is unknown, but clinical syndromes caused by this organism are common. Bacteremia, pneumonia, endocarditis, and bone and joint infections are encountered with relative frequency in this population, and the clinical presentation may be atypical. Underlying disease and functional debility, rather than age itself, predispose the older adult to staphylococcal carriage and infection. Infections with methicillin-resistant strains of S. aureus are acquired primarily in hospital, rather than in nursing homes or in the community. Lack of clinical suspicion for S. aureus infection and delays in appropriate therapy can be fatal. Staphylococcal infection should be considered for an older adult with risk factors for staphylococcal carriage, comorbid illness, debility, and history of recent hospitalization or nursing home stay. Choices regarding empirical therapy should be made on the basis of knowledge of local antibiotic susceptibility patterns.

Economic evaluation of linezolid, flucloxacillin and vancomycin in the empirical treatment of cellulitis in UK hospitals: a decision analytical model

Standard antibiotic treatment of infections has become more difficult and costly due to treatment failure associated with the rise in bacterial resistance. New antibiotics that can overcome such resistant pathogens have the potential for great clinical and economic impact. Linezolid is a new antibiotic that is effective in the treatment of both antibiotic-susceptible and antibiotic-resistant Gram-positive bacterial infections, including those resistant to other available antibiotics. This breadth of activity is unique in existing antibiotics for Gram-positive bacteria and serves as the rationale for exploring the hypothesis that linezolid is an appropriate choice when considering empirical treatment of cellulitis in complicated or compromised patients in the nosocomial setting. A decision-modelling approach was used to compare the predicted first-line treatment efficacy and direct medical costs of linezolid with standard treatment of cellulitis among hospitalized patients. For the purposes of this analysis, standard care is defined along two main pathways: (1) initiating care with intravenous (iv) flucloxacillin, switching to vancomycin if the pathogen is found to be resistant to flucloxacillin, or maintaining flucloxacillin if the pathogen is found susceptible, or when culture and sensitivity analysis is inconclusive; or (2) initiating care with vancomycin, switching to iv flucloxacillin if the pathogen is found susceptible to flucloxacillin, maintaining vancomycin if the infection is found resistant, or when culture and sensitivity are inconclusive. For those patients taking iv flucloxacillin, a switch to oral flucloxacillin was allowed when clinically appropriate. We hypothesized that the cost of care of initiating treatment with linezolid would be less than that for both vancomycin and flucloxacillin in resistance risk ranges typically encountered in UK hospitals. In addition, while the registration trials showed equivalence of linezolid with the comparators in known or suspected methicillin-resistant Staphylococcus aureus (MRSA) and in known or suspected methicillin-susceptible Staphylococcus aureus (MSSA) (vancomycin and oxacillin) respectively, we hypothesized that first-line success rates would be higher in empiric treatment with linezolid. Efficacy data were obtained from recent clinical trials with linezolid and standard treatment, and medical resource utilization was obtained from an expert panel of clinicians who were questioned regarding resistant and susceptible infections separately. UK hospital direct medical costs of treatment were determined using standard costing techniques. Base case analyses assumed a residual 80% unknown pathogen rate after culture and susceptibility based on a physician survey and supported in the literature. The analysis in this model predicts that initiating empirical treatment of cellulitis with linezolid will (1) result in higher overall success rates than flucloxacillin for first-line treatment, regardless of resistance risk and (2) be less costly than initiating treatment with flucloxacillin when the likelihood of a patient being infected by a resistant pathogen is greater than 24.1%. Furthermore, initiating treatment with linezolid is predicted to result in higher overall success rates and be less costly than vancomycin across the entire spectrum of the patients' risk of being infected by a resistant pathogen.

Rapid identification of methicillin-resistant Staphylococcus aureus from positive blood cultures by real-time fluorescence PCR

Methicillin-resistant Staphylococcus aureus septicemia is associated with significant morbidity and mortality and requires treatment with intravenous glycopeptides. For blood cultures positive for gram-positive cocci, 24 to 48 h is required for the detection of S. aureus bacteremia and the provision of antibiotic susceptibility testing results. We describe a molecular biology-based assay that requires 2 h from the time of initial positivity of blood cultures. The assay correctly detected 96% of the S. aureus isolates including all methicillin-resistant S. aureus isolates. Clinical data collected during the study suggest that 28% of patients with S. aureus bacteremia do not receive early and appropriate treatment and that 10% of patients may initially be receiving inappropriate glycopeptide treatment.

Economic impact and formulary positioning of linezolid: a new anti-Gram-positive antimicrobial

Gram-positive bacteria have emerged as major causes of colonization and serious infection within the nosocomial and increasingly also within the community setting. These infections have significantly contributed to patient morbidity and mortality as well as prolongation of hospital stay, a key determinant of the cost of an episode of infection in hospital. In many countries globally, infections due to methicillin-resistant Staphylococcus aureus (MRSA) are providing the greatest burden of clinical infection, often occurring in vulnerable patients or "high risk" therapeutic settings. Combined with this scenario is the increasing requirement for health care organizations to provide cost-effective health care as well as care that is delivered on evidence-based practice delivered through formularies or guidelines. This article aims to: 1) summarize the key economic considerations pertinent to these multiresistant infections but with an emphasis on MRSA, 2) discuss the current therapeutic options of managing MRSA infections, and 3) discuss the formulary positioning of linezolid by means of outlining its core strengths, weaknesses and the opportunity it provides to hospital infection management.

De-escalation antimicrobial chemotherapy in critically III patients: pros and cons

In spite of advances in critical care, nosocomial infections still have a considerable impact on Intensive Care Unit (ICU) and hospital length of stay, mortality and costs. Several authors suggest that antibiotic therapy should be instituted as soon as sepsis is suspected in critically patients. Over the last two decades the rates of occurrence for pathogens have significantly changed under selective pressure from broad-spectrum antimicrobial therapy. Shifts from predominance of gram-negative to gram-positive organisms and outbreaks of resistant pathogens address the need for appropriate empirical regimens. Agents such as ceftazidime, imipenem and, more recently, meropenem and tazobactam have been used successfully as monotherapy. Two different clinical trials have reported that meropenem monotherapy is significantly more effective than ceftazidime-based therapy. Because of the outbreak of methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis, some investigators suggest adding a glycopeptide to beta-lactamase inhibitor and carbapenem as initial empirical therapy. Such a regimen should be administered before definitive proof of infections and until the results of microbial investigation are available (de-escalation antimicrobial chemotherapy). On the other hand, several authors do not recommend glycopeptide administration in an attempt to limit nosocomial outbreaks of vancomycin-resistant enterococci (VRE) and staphylococci (VRS) and to avoid secondary drawbacks, such as nephrotoxicity and ototoxicity. De-escalation antimicrobial chemotherapy should be tailored to critically ill patients according to their clinical status, severity of illness and suspicion of sepsis or nosocomial pneumonia.

Therapy of nosocomial pneumonia

HAP remains a major cause of morbidity and mortality among hospitalized patients. Although early appropriate therapy results in improved outcomes, the cause of HAP frequently is not known at the time antimicrobial therapy is initiated. Most cases of HAP result from microaspiration of oropharyngeal secretions previously colonized with pathogenic bacteria, and the spectrum of potential pathogens is broad. Taking several factors into account can narrow this spectrum, including severity of illness, length of stay before the onset of pneumonia, and presence of risk factors for specific pathogens. When therapy has been initiated, follow-up of microbial studies and careful monitoring of the patient's course is important. The clinical improvement, even when therapy is appropriate, frequently takes days; therapy should not be changed for the first 2 to 3 days unless frank deterioration is noted. Patients who fail to respond or experience clinical deterioration should be re-examined carefully, and thought should be given to the possibility of other noninfectious processes.

[Impact of bacterial resistance on severe infections]

Since many years, the antimicrobial resistance increases as well as for community-acquired as for nosocomial infections. Antibiotic-resistant pneumococci are neither more nor less virulent susceptible strains. Except for immunocompromised patients, the outcome of penicillin-resistant pneumococcal infections have been similar to those in patients who are infected by susceptible ones. Current levels of S. pneumoniae resistance to penicillin and cephalosporin are not associated to an increase in mortality in children with meningitis if adequate doses of antibiotics are given. Because empiric therapy has changed, antibiotic resistance has not been associated with increased mortality. This statement can be extended to Meningococcus, for which 32 to 50% of the strains have a decreased susceptibility to penicillin. For nosocomial infections, S. aureus is the main studied pathogen. Several studies report that in patients with severe diseases (bacteremia or pneumonia) methicillin resistance of S. aureus had no significant impact on patient outcome after adjustment for different confounders. The main risk factor for mortality is the severe underlying diseases rather than the resistance as well for methicillin--resistant S. aureus, as for vancomycin resistant enterococci, Klebsiella with extended spectrum beta lactamase and Enterobacters. Recommendations for controlling epidemiologic surveillance, using barrier precautions and limiting the use of antibiotics as well in the hospital as in the community must be undertaken.

How to organise antibiotic prescription

In recent years, efforts have been made in hospitals to improve antibiotic prescription. Most universities organise courses on the subject, which lead to a local university diploma. However, possessing such a diploma does not give entitlement to prescribe. In fact, most doctors prescribe antibiotics and such courses are only of interest to volunteer physicians. While some are very careful, the majority prescribe the drugs as they are rarely toxic. Others are refractory to any information and particularly to any training. Two methods are typically proposed to reduce unjustified prescription. As a result of imposed restrictions, only trained doctors having met the training standards are allowed to prescribe and have to keep to a limited budget. The persuasive method, on the other hand, opens the way for a wide scope of training courses, which are provided by industry; some are said to be biased as they encourage prescription and the risk of selecting resistant mutant bacteria is scarcely documented. This method does not always coincide with the training curricula. The industry is torn between declared objectives such as judicious drug use and prevailing commercial aims. As a result, prescription is not restrained by any objective limit. It should be noted that prescription varies greatly from one hospital to another and within a given hospital between one department and another. Certain departments prescribe much more than others and these (emergency, medical and surgical intensive care, respiratory disease) should be targeted first.

International Conference for the Development of Consensus on the Diagnosis and Treatment of Ventilator-associated Pneumonia

Ventilator-associated pneumonia (VAP) is an important health problem that still generates great controversy. A consensus conference attended by 12 researchers from Europe and Latin America was held to discuss strategies for the diagnosis and treatment of VAP. Commonly asked questions concerning VAP management were selected for discussion by the participating researchers. Possible answers to the questions were presented to the researchers, who then recorded their preferences anonymously. This was followed by open discussion when the results were known. In general, peers thought that early microbiological examinations are warranted and contribute to improving the use of antibiotherapy. Nevertheless, no consensus was reached regarding choices of antimicrobial agents or the optimal duration of therapy. Piperacillin/tazobactam was the preferred choice for empiric therapy, followed by a cephalosporin with antipseudomonal activity and a carbapenem. All the peers agreed that the pathogens causing VAP and multiresistance patterns in their ICUs were substantially different from those reported in studies in the United States. Pathogens and multiresistance patterns also varied from researcher to researcher inside the group. Consensus was reached on the importance of local epidemiology surveillance programs and on the need for customized empiric antimicrobial choices to respond to local patterns of pathogens and susceptibilities.

Multi-resistance to antimicrobial agents for the ten most frequently isolated bacterial pathogens

Cross-resistance and multi-resistance to selected antibiotics was determined for Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Amikacin-resistant Enterobacteriaceae often showed cross-resistance to ss-lactam antibiotics. Only 1% of the Escherichia coli isolates showed resistance to more than four antibiotics from a set of seven. This rate was higher for other Enterobacteriaceae and there were high levels of cross-resistance for P. aeruginosa. The cross-resistance of oxacillin with other antibiotics is well known in staphylococci. Penicillin-resistant pneumococcal isolates were cross-resistant to macrolides. Cross-resistance was only a minor problem in H. influenzae and M. catarrhalis. Cross- and multi-resistance are important problems for Gram-negative and Gram-positive bacteria but not for fastidious bacteria with the exception of penicillin-resistant S. pneumoniae.

Impact of Gram-positive resistance on outcome of nosocomial pneumonia

Among Gram-positive pathogens, Staphylococcus aureus is the leading cause of death from nosocomial pneumonia. The bacterium developed progressive resistance to beta-lactams, and methicillin-resistant strains emerged in the 1980s. In consequence, vancomycin has become the drug of choice for treatment of this infection over the last decade, based on susceptibility tests and the serum antimicrobial levels recorded. However, half of the patients treated with vancomycin have died. In contrast, in patients receiving beta-lactams for pneumonia caused by methicillin-sensitive S. aureus, survival is the rule. These observations, together with the emergence of isolates with reduced susceptibility to glycopeptides, raised concern about the use of vancomycin as standard therapy for pneumonia caused by Gram-positive cocci. Maintaining tissue levels above minimal inhibitory concentration is vital to successful clinical outcome. Optimizing treatment focusing on this goal and new antimicrobials provide new opportunities to improve survival. (Crit Care Med 2001; 29[Suppl.]:N82-N86)

Impact of antibiotic resistance on clinical outcomes and the cost of care

Antibiotic-resistant organisms are common in intensive care unit infection and can be either Gram-positive or Gram-negative. A number of studies have evaluated whether these organisms can lead to excess morbidity, mortality, or cost. In general, the studies are confounded by a number of methodologic issues, including the selection of an appropriate control population. Cases and controls must be appropriately matched for the presence of infection, the presence of infection with similar organisms (but ones that are either antibiotic-sensitive or -resistant), and severity of illness. In addition, studies must account for the therapies given to patients who are infected with resistant organisms because resistance is an important risk factor for inadequate empirical therapy, and such therapy is itself a potent determinant of a number of adverse outcomes, including mortality. To date, the data with methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococcus are inconsistent with regard to the effect on mortality rates, although infection with both organisms can lead to excess length of stay and increased cost of care. When studies have been adequately controlled and powered, infection with vancomycin-resistant enterococcus has had more of an effect on the mortality rate than infection with antibiotic-sensitive enterococci. Infection with resistant Gram-negatives also has adverse impact on outcome, with excess mortality being seen in patient groups infected with Acinetobacter and Pseudomonas aeruginosa. If we are to minimize the effect of resistance on medical outcomes and cost, it will be necessary to have a current knowledge of each intensive care unit's pathogens and susceptibility patterns, so that empirical therapy will have a good likelihood of being effective. In addition, new therapeutic agents may improve on the efficacy of older agents and could reduce cost if they allow for some patients to leave the hospital and to finish therapy with an oral formulation of a highly bioavailable agent.

Is there a role for antibiotic cycling in the intensive care unit?

Antibiotic resistance of bacterial pathogens has emerged as one of the most important issues facing critical care practitioners. Resistance of many commonly encountered bacterial species is increasing and has been associated with greater administration of inadequate antimicrobial therapy to patients within intensive care units. This has resulted in greater patient morbidity, higher mortality rates, and increased healthcare costs. Methods to reduce antimicrobial resistance have focused on increasing adherence to infection control practices and improving antibiotic utilization. Antibiotic cycling is a strategy to reduce antimicrobial resistance by withdrawing an antibiotic or antibiotic class from use and subsequently reintroducing it at a later point in time. The main goal of cycling is to allow resistance rates for specific antibiotics to decrease, or at least remain stable, when their use is periodically eliminated from the intensive care unit.

Antibacterial activity of 41 antimicrobials tested against over 2773 bacterial isolates from hospitalized patients with pneumonia: I--results from the SENTRY Antimicrobial Surveillance Program (North America, 1998)

Pneumonia is the second most frequent cause of nosocomial infection, and hospitalization frequently is needed for community-acquired pneumonia. Knowledge of causative pathogens through periodic surveillance, and their prevailing antimicrobial susceptibility patterns becomes paramount in choosing appropriate empiric therapy. The SENTRY Antimicrobial Surveillance Program, tracks pathogen distribution worldwide since 1997 and documents emerging resistance to a wide range of antimicrobial agents. During the respiratory disease season in 1998, each of 30 medical centers (25 in the United States [US], and five in Canada [CAN]) contributed 100 consecutive isolates obtained from hospitalized patients with suspected pneumonia. The 2773 organisms, processed by the monitor consisted of a total of 35 species, with Staphylococcus aureus comprising 25.6% of all isolates and five other species (Pseudomonas aeruginosa 18.7%, Haemophilus influenzae 9.4%, Streptococcus pneumoniae 7.8%, Klebsiella spp. 7.0%, and Enterobacter spp. 6.7%) making up almost 50% of the total. In the US, pneumococci (8.5%) were more prevalent than in CAN (4.1%; p = 0.001). The US isolates of S. pneumoniae were variably susceptible to penicillin (76.8%), with non-susceptible strains demonstrating greater levels of cross resistance to macrolides (31.8%), cefepime (9.0%) and cefotaxime (6.8%), but remaining susceptible to gatifloxacin and quinupristin/dalfopristin. H. influenzae and Moraxella catarrhalis were generally ampicillin-resistant, 40.4-44.4% and 93.7-95.7%, respectively. P. aeruginosa remained very susceptible to amikacin (91.3-93.8%) > tobramycin > meropenem > piperacillin/tazobactam > gentamicin > piperacillin > cefepime (80.0-81.8%). Extended spectrum beta-lactamase phenotypes among the Klebsiella spp. were isolated from five medical centers in the US and were 4.8-6.0% overall; a rate similar to the previous year. Among the US isolates of Enterobacter spp., only 77.6% and 79.6% were susceptible to ceftazidime and cefotaxime, respectively, but >90% were inhibited by cefepime, imipenem, meropenem, aminoglycosides, and fluoroquinolones. Isolates from CAN were generally more susceptible, except for Pseudomonas isolates, where resistance to aminoglycosides, fluoroquinolones and imipenem was greater. The SENTRY Program results outline important national differences in the frequencies of pathogen occurrence, but more importantly, identify unstable patterns of resistance to available antimicrobial drugs, and serves as a reference for results of other local, national or international investigations.

Hospital-acquired pneumonia: risk factors, microbiology, and treatment

Pneumonia complicates hospitalization in 0.5 to 2.0% of patients and is associated with considerable morbidity and mortality. Risk factors for hospital-acquired pneumonia (HAP) include mechanical ventilation for > 48 h, residence in an ICU, duration of ICU or hospital stay, severity of underlying illness, and presence of comorbidities. Pseudomonas aeruginosa, Staphylococcus aureus, and Enterobacter are the most common causes of HAP. Nearly half of HAP cases are polymicrobial. In patients receiving mechanical ventilation, P aeruginosa, Acinetobacter, methicillin-resistant S aureus, and other antibiotic-resistant bacteria assume increasing importance. Optimal therapy for HAP should take into account severity of illness, demographics, specific pathogens involved, and risk factors for antimicrobial resistance. When P aeruginosa is implicated, monotherapy, even with broad-spectrum antibiotics, is associated with rapid evolution of resistance and a high rate of clinical failures. For pseudomonal HAP, we advise combination therapy with an antipseudomonal beta-lactam plus an aminoglycoside or a fluoroquinolone (eg, ciprofloxacin).

Benefits of negative penicillin skin test results persist during subsequent hospital admissions

For an initial series of 38 patients with negative skin test results, we reviewed retrospectively all subsequent admissions over a 2-year period. For 38 patients with negative initial skin test results, there were 48 subsequent readmissions to our institution, of which 35 required antibiotics. beta-lactams were prescribed for 86% of admissions; a penicillin for 37%, and a cephalosporin for 51%. All infections were cured, and there were no allergic drug reactions during any of the admissions that were reviewed.

Clonal associations among Staphylococcus aureus isolates from various sites of infection

A molecular epidemiological analysis was undertaken to identify lineages of Staphylococcus aureus that may be disproportionately associated with infection. Pulsed-field gel electrophoresis analysis of 405 S. aureus clinical isolates collected from various infection types and geographic locations was performed. Five distinct S. aureus lineages (SALs 1, 2, 4, 5, and 6) were identified, which accounted for 19.01, 9.14, 22.72, 10.12, and 4.69% of isolates, respectively. In addition, 85 lineages which occurred with frequencies of <2.5% were identified and were termed "sporadic." The most prevalent lineage was methicillin-resistant S. aureus (SAL 4). The second most prevalent lineage, SAL 1, was also isolated at a high frequency from the anterior nares of healthy volunteers, suggesting that its prevalence among clinical isolates may be a consequence of high carriage rates in humans. Gene-specific PCR was carried out to detect genes for a number of staphylococcal virulence traits. tst and cna were found to be significantly associated with prevalent lineages compared to sporadic lineages. When specific infection sites were examined, SAL 4 was significantly associated with respiratory tract infection, while SAL 2 was enriched among blood isolates. SAL 1 and SAL 5 were clonally related to SALs shown by others to be widespread in the clinical isolate population. We conclude from this study that at least five phylogenetic lineages of S. aureus are highly prevalent and widely distributed among clinical isolates. The traits that confer on these lineages a propensity to infect may suggest novel approaches to antistaphylococcal therapy.

Economic impact of antimicrobial resistance

One reason antimicrobial-drug resistance is of concern is its economic impact on physicians, patients, health-care administrators, pharmaceutical producers, and the public. Measurement of cost and economic impact of programs to minimize antimicrobial-drug resistance is imprecise and incomplete. Studies to describe and evaluate the problem will have to employ new methods and be of large scale to produce information that is broadly applicable.

Molecular analysis of methicillin-resistant Staphylococcus aureus as a causative agent of bronchopulmonary infection: relation to colonization in the upper respiratory tract

Using five diagnostic markers, we compared the types of 72 strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated simultaneously from the nasal cavity, pharynx, and sputum from 24 patients. Almost identical MRSA types had colonized the nasal cavity and sputum from the same patient for 21 (88%) of the patients. We speculate that most MRSA organisms isolated in sputum are derived from the nasal cavity, while a few are derived from the pharynx.

Gram-Positive Pneumonia

Gram-positive pneumonia is a leading cause of morbidity and mortality throughout the world. Of the gram-positive pathogens that cause pneumonia, Streptococcus pneumoniae and Staphylococcus aureus are the most common. The diagnosis of gram-positive pneumonia remains less than satisfactory, and newer diagnostic techniques such as antibody- and polymerase chain reaction-based antigen detection have yet to prove themselves. Drug resistance among gram-positive organisms is now endemic throughout the world and remains a serious therapeutic problem despite the availability of new antimicrobials. Efforts to control the spread of resistant strains include, in the case of S. aureus, stringent isolation policies and topical treatment to reduce carriage and, for S. pneumoniae, increased use of available vaccines and the develop- ment of more immunogenic vaccines.