Cefepime versus ceftriaxone for empiric treatment of hospitalized patients with community-acquired pneumonia. The Cefepime Study Group

Pseudomonas fluorescens pneumonia

Pseudomonas fluorescens (P. fluorescens) is not generally considered a bacterial pathogen in humans; however, multiple culture-based and culture-independent studies have identified it in the indigenous microbiota of multiple body sites. We herein report a rare case of pneumonia caused by P. fluorescens. A man in his 80 s with chronic obstructive pulmonary disease and diabetes mellitus was diagnosed with stage II rectal cancer. He underwent laparoscopic surgery, and on the 6th postoperative day, he developed a high fever. Chest computed tomography revealed infiltration in the left lower lung. Gram staining of the sputum showed Gram-negative rods phagocytosed by neutrophils, suggesting postoperative nosocomial pneumonia. The patient was started on tazobactam/piperacillin, and his pneumonia quickly improved. Later, only P. fluorescens was detected in a sputum culture. It was susceptible to common antipseudomonal agents. Gram staining of P. fluorescens appears to show a slightly thicker and larger morphology in comparison to Pseudomonas aeruginosa. Although there have been reports of opportunistic infections caused by P. fluorescens in immunosuppressed patients, including those with advanced cancer, most have been bloodstream infections, with very few reports of pneumonia alone. Clinicians should be aware that patients, who are not necessarily immunosuppressed, may develop pneumonia caused by P. fluorescens.

Pneumonia caused by Pseudomonas fluorescens: a case report

BACKGROUND

Pseudomonas fluorescens (P. fluorescens) has been detected in respiratory samples from patients. However, no previous reports have been published about these P. fluorescens cultures from lung tissues.

CASE PRESENTATION

Here, we report a case of pneumonia caused by P. fluorescens. P. fluorescens was identified from lung biopsy specimens for the first time in this case. According to the antibiotic susceptibility testing (AST) of P. fluorescens, the patient was given ciprofloxacin treatment. The temperature of the patient then returned to normal. Chest CT examination revealed improvements in pulmonary inflammation.

CONCLUSIONS

These findings suggest that the patients with pneumonia caused by P. fluorescens should be treated in a timely manner according to the AST results.

Efficacy of Ceftriaxone 1 g daily Versus 2 g daily for The Treatment of Community-Acquired Pneumonia: A Systematic Review with Meta-Analysis

Introduction: Ceftriaxone has been recommended as a first-line treatment for various infections; however, the doses for pneumonia have not been a consensus in randomized clinical trials. To compare ceftriaxone 1 g daily efficacy to other ceftriaxone dosing regimens in community-acquired pneumonia. Area covered: We performed a systematic review and meta-analysis on PubMed, Web of Science, Scopus, and LILACS. Randomized controlled trials of ceftriaxone in community-acquired pneumonia were included. Outcomes included clinical cure in modified intention-to-treatment, clinically and microbiologically evaluable patients. Expert opinion: Ceftriaxone dosages of 1 g daily are as safe and effective as other antibiotic regimens for community-acquired pneumonia. Twenty-four articles fulfilled the inclusion criteria. Twelve studies evaluated ceftriaxone regimens at a dosage of 2 g daily and 12 studies evaluated ceftriaxone at a dosage of 1 g daily. The odds-ratio of clinical cure in the modified intention-to-treatment patients administered either ceftriaxone (4666 patients) or a comparator (4411 patients) was 0.98 (95% CI [0.82-1.17]). Comparator regimens showed similar efficacy to ceftriaxone regimens of 1 g daily, with an odds ratio of 1.03 (95% CI [0.88-1.20]). Dosages higher than ceftriaxone 1 g daily did not result in improved clinical outcomes for community-acquired pneumonia patients (OR 1.02, 95% CI [0.91-1.14]).

Microbiology, genomics, and clinical significance of the Pseudomonas fluorescens species complex, an unappreciated colonizer of humans

Pseudomonas fluorescens is not generally considered a bacterial pathogen in humans; however, multiple culture-based and culture-independent studies have identified it at low levels in the indigenous microbiota of various body sites. With recent advances in comparative genomics, many isolates originally identified as the "species" P. fluorescens are now being reclassified as novel Pseudomonas species within the P. fluorescens "species complex." Although most widely studied for its role in the soil and the rhizosphere, P. fluorescens possesses a number of functional traits that provide it with the capability to grow and thrive in mammalian hosts. While significantly less virulent than P. aeruginosa, P. fluorescens can cause bacteremia in humans, with most reported cases being attributable either to transfusion of contaminated blood products or to use of contaminated equipment associated with intravenous infusions. Although not suspected of being an etiologic agent of pulmonary disease, there are a number of reports identifying it in respiratory samples. There is also an intriguing association between P. fluorescens and human disease, in that approximately 50% of Crohn's disease patients develop serum antibodies to P. fluorescens. Altogether, these reports are beginning to highlight a far more common, intriguing, and potentially complex association between humans and P. fluorescens during health and disease.

Cefepime

Cefepime (Maxipime), Maxcef, Cepimax, Cepimex, Axepim, a parenteral fourth-generation cephalosporin, is active against many organisms causative in pneumonia. Cefepime has in vitro activity against Gram-positive organisms including Staphylococcus aureus and penicillin-sensitive, -intermediate and -resistant Streptococcus pneumoniae similar to that of cefotaxime and ceftriaxone. Cefepime also has good activity against Gram-negative organisms, including Pseudomonas aeruginosa, similar to that of ceftazidime. Importantly, cefepime is stable against many of the common plasmid- and chromosome-mediated beta-lactamases and is a poor inducer of AmpC beta-lactamases. As a result, it retains activity against Enterobacteriaceae that are resistant to third-generation cephalosporins, such as derepressed mutants of Enterobacter spp. Cefepime may be hydrolyzed by the extended-spectrum beta-lactamases produced by some members of the Enterobacteriaceae, but to a lesser extent than the third-generation cephalosporins. Monotherapy with cefepime 1 or 2g, usually administered intravenously twice daily, was as effective for clinical and bacteriological response as ceftazidime, ceftriaxone or cefotaxime monotherapy (1 or 2g two or three times daily) in a number of randomized, clinical trials in hospitalized adult, or less commonly, pediatric, patients with generally moderate to severe community-acquired or nosocomial pneumonia. More limited data indicated that monotherapy with cefepime 2g three times daily was also as effective in treating patients with nosocomial pneumonia as imipenem/cilostatin 0.5g four times daily, and when combined with amikacin, cefepime was as effective as ceftazidime plus amikacin. Patients with pneumonia who failed to respond to previous antibacterial therapy with penicillins or other cephalosporins responded to treatment with cefepime. Cefepime is generally well tolerated, with a tolerability profile similar to those of other parenteral cephalosporins. In clinical trials, the majority of adverse events experienced by cefepime recipients were mild to moderate and reversible. The most common adverse events with a causal relationship to cefepime reported in clinical trials included rash and diarrhea. Other, less common, adverse events included pruritus, urticaria, nausea, vomiting oral candidiasis, colitis, headache, fever, erythema and vaginitis.

CONCLUSION

Cefepime is an established and generally well tolerated parenteral drug with a broad spectrum of antibacterial activity which, when administered twice daily, provides coverage of most of the pathogens that may be causative in pneumonia. In randomized clinical trials in hospitalized patients with generally moderate to severe community-acquired or nosocomial pneumonia, cefepime monotherapy exhibited good clinical and bacteriological efficacy. Cefepime may become a preferred antibacterial agent for infections caused by Enterobacter spp. With prudent use in order to prevent the emergence of resistant organisms, cefepime will continue to be a suitable option for the empiric treatment of pneumonia.

Oral infections and antibiotic therapy

Oral infections commonly originate from an odontogenic source in adults and from tonsil and lymphatic sources in children. Odontogenic infections arise from advanced dental caries or periodontal disease. Oral trauma, radiation injury, chemotherapy mucositis, salivary gland infection, lymph node abscess, and postoperative infection are potential nonodontogenic sources of infections that could potentially be life threatening. This article reviews the serious nature and potential danger that exists from oral infection and the antibiotics available to treat them are reviewed. Successful treatment requires an understanding of the microflora, the regional anatomy, the disease process, the treatment methods available, and interdisciplinary team collaboration.

Efficacy and safety of cefepime: a systematic review and meta-analysis

Cefepime is a broad-spectrum cephalosporin with enhanced coverage against Gram-positive and Gram-negative bacteria. We did a systematic review of randomised trials that compared cefepime with another beta-lactam antibiotic, alone or with the addition of a non-beta-lactam antibiotic to both study groups. We searched Central, PubMed, Embase, Lilacs, new US Food and Drug Administration drug applications, conference proceedings, and references of the included studies. Two reviewers independently did the search and data extraction. 57 trials were included. All-cause mortality-the primary outcome-was higher with cefepime than other beta-lactams (risk ratio [RR] 1.26 [95% CI 1.08-1.49]). Sensitivity analyses by the trials' methodological quality revealed higher RRs for trials reporting adequate allocation-sequence generation (1.52 [1.20-1.92]) and allocation concealment (1.36 [1.09-1.70]). Baseline risk factors for mortality were similar. No significant differences between groups in treatment failure, superinfection, or adverse events were found. This Review provides evidence and offers possible explanations for increased mortality among patients treated with cefepime in randomised trials.

Once-Daily Cefepime Versus Ceftriaxone for Nursing Home–Acquired Pneumonia

OBJECTIVES

To compare once-daily intramuscular cefepime with ceftriaxone controls.

DESIGN

Double-blind study.

SETTING

Six skilled nursing facilities.

PARTICIPANTS

Residents aged 60 and older with nursing home-acquired pneumonia.

INTERVENTION

Cultures were obtained, and patients were randomized to cefepime or ceftriaxone 1 g intramuscularly every 24 hours.

MEASUREMENTS

Clinical success: cure or improvement. Cure was defined as complete resolution of all symptoms and signs of pneumonia or a return to the patient's baseline state. Improvement was defined as clear improvement but incomplete resolution of all pretherapy symptoms or signs or incomplete return to the patient's usual baseline status. Safety and pharmacoeconomics were also assessed.

RESULTS

Sixty-nine patients were randomized; 61 were evaluable: (32 to cefepime, 29 ceftriaxone). Patients were predominately female (76%). They had a mean age+/-standard deviation of 85+/-6, with a mean 5.8+/-1.9 comorbidities; they had age-appropriate renal dysfunction, with a mean estimated creatinine clearance of 35+/-7 mL/min. Clinical success occurred in 78% of cefepime- and 66% of ceftriaxone-treated patients (P=.39). Fifty-seven patients (93%) were switched to oral antibiotics after 3 days. Antibiotic-related adverse events occurred in 5% of patients. Seven patients (11.5%) were hospitalized. The overall mortality rate was 8%. Mean antibiotic costs were 117+/-40 dollars for cefepime- and 215+/-68 dollars for ceftriaxone-treated patients (P<.001). Cost-effectiveness analysis of total costs showed that cefepime would cost 597 dollars and ceftriaxone 1,709 dollars per expected successfully treated patient. One- and two-way sensitivity analyses using a generic price for ceftriaxone and improving its comparative efficacy revealed that the results were robust.

CONCLUSIONS

Once-daily cefepime was a cost-effective alternative to ceftriaxone for the treatment of elderly nursing home residents who developed pneumonia and did not require hospitalization.

Comparative adherence to human A549 cells, plant fibronectin-like protein, and polystyrene surfaces of fourPseudomonas fluorescensstrains from different ecological origin

The main objective of this study was to compare the adherence properties of four Pseudomonas fluorescens isolates from different ecological niches (human tissue, rhizosphere, drinking water, and cow milk). The substrates used to test P. fluorescens adherence were as follows: cultured human respiratory epithelial cells A549, immobilized plant fibronectin-like protein, and polystyrene. For all the experiments, bacteria were grown at 27 °C. The adherence assay to human cells was performed at 37 °C, whereas adherence to fibronectin and polystyrene was done at 27 °C. The four strains tested adhered to A549 cells but showed different adherence patterns. At 3 h, the milk isolate showed an aggregative adherence phenotype, whereas the three other isolates showed a diffuse adherence pattern. With a longer incubation time of 24 h, the aggregative pattern of the milk isolate disappeared, the adherence of the clinical strain increased, the adherence of the water isolate decreased, and morphological changes in A549 cells were observed with the clinical, water, and soil isolates. The four strains tested formed biofilms on polystyrene dishes. The clinical and milk isolates were the more efficient colonizers of polystyrene surfaces and also the more adherent to immobilized plant fibronectin-like protein. There was no relation between bacterial surface hydrophobicity and P. fluorescens adherence to the substrates tested. The main conclusions of these results are that P. fluorescens is an adherent bacterium, that no clear correlation exists between adherence and ecological habitat, and that P. fluorescens can adhere well to substrates not present in its natural environment.Key words: Pseudomonas fluorescens, adherence, biofilm, ecological niche, plant fibronectin-like protein, A549, polystyrene.

Cefepime versus ceftazidime for treatment of pneumonia

Consecutive patients with pneumonia, treated with cefepime (n = 66) or ceftazidime (n = 132), were evaluated in a retrospective, observational study. There was no significant difference between the two treatment groups with respect to age, underlying diseases, acute physical and chronic health evaluation score, intensive care unit admission, presence of sepsis, community or hospital acquisition, causative organism, duration of therapy, death, cure or improvement in infection, adverse events, superinfections, presence of vancomycin-resistant enterococcus (VRE) and resistance to therapy. Post-therapy hospitalization (days) and vancomycin co-administration were significantly lower, and time to vancomycin initiation significantly higher, in the cefepime compared with the ceftazidime group. The results suggest a trend towards less resistance on therapy, less VRE, reduced vancomycin use and shorter post-therapy hospitalization in patients treated with cefepime compared with ceftazidime. The clinical outcomes for hospitalized patients treated for serious pneumonia were similar between the two groups.

In vitro identification of two adherence factors required for in vivo virulence of Pseudomonas fluorescens

By enriching a random transposon insertion bank of Pseudomonas fluorescens for mutants affected in their adherence to the human extracellular matrix protein fibronectin, we isolated 23 adherence minus mutants. Mutants showed a defect in their ability to develop a biofilm on an abiotic surface and were impaired for virulence when tested in an in vivo virulence model in the fruit fly, Drosophila melanogaster. Molecular characterisation of these mutants showed that the transposon insertions localised to two distinct chromosomal locations, which were subsequently cloned and characterised from two mutants. A search in the databanks identified two loci in the Pseudomonas aeruginosa PAO1 genome with significant homology to the genes interrupted by the transposon insertions. Mutant IVC6 shows homology to gmd, coding for the enzyme GDP-mannose dehydratase, involved in the synthesis of A-band- O-antigen-containing lipopolysaccharide (LPS). Mutant IVG7 is significantly similar to a probable outer membrane protein of strain PAO1, with no specific function attributed thus far, yet with significant homology to Escherichia coli FadL, involved in long-chain fatty acid transport. We propose that this protein, together with LPS, is involved in the first steps of P. fluorescens adherence leading to host colonisation. Results presented here also demonstrate the pathogenic potential of P. fluorescens, assessed in an in vivo Drosophila model system, correlated with its ability to adhere to the human extracellular matrix protein, fibronectin. Correlation between the mutant phenotypes with identified virulence factors and their actual role in the virulence of P. fluorescens is discussed.

Ertapenem Therapy for Community-Acquired Pneumonia in the Elderly

OBJECTIVES

To compare the efficacy and safety of ertapenem, 1 g once a day, with ceftriaxone, 1 g once a day, for treatment of the subgroup of patients aged 65 and older with community-acquired pneumonia (CAP) requiring parenteral therapy.

DESIGN

Combined data from patients aged 65 and older in two randomized, double-blind clinical trials.

SETTING

Eighty international centers.

PARTICIPANTS

Eight hundred fifty-seven treated patients, of whom 351 were aged 65 and older.

INTERVENTIONS

Intravenous or intramuscular ertapenem or ceftriaxone with the option to switch to oral amoxicillin-clavulanate after at least 3 days of parenteral therapy.

MEASUREMENTS

Clinical efficacy was assessed at completion of parenteral therapy and 7 to 14 days after all therapy had been completed (test of cure (TOC) assessment). Bacterial eradication was assessed at the TOC visit. Safety was assessed daily during study therapy and for 14 days thereafter.

RESULTS

One hundred forty-eight clinically evaluable patients aged 65 and older were treated with ertapenem and 125 with ceftriaxone. Pathogens were identified in 157 (57.5%) patients (the most common being Streptococcus pneumoniae), most of which were penicillin-susceptible. Clinical cure rates were 95.9% for patients in the ertapenem group and 92.7% for patients in the ceftriaxone group at completion of parenteral therapy and 93.9% and 90.4%, respectively, at the TOC assessment. Overall bacterial eradication rates were 92.8% (77 of 83) for patients treated with ertapenem and 93.2% (69 of 74) for those treated with ceftriaxone. The most common drug-related adverse experiences in both treatment groups were diarrhea and mild to moderate elevation of serum aminotransferase levels.

CONCLUSION

Ertapenem 1 g once a day was highly effective for treatment of elderly patients with CAP requiring parenteral therapy and was as effective as ceftriaxone. Ertapenem was generally well tolerated, with an overall safety profile similar to ceftriaxone.

Comparative in vitro activity of ertapenem against bacterial pathogens isolated from patients with lower respiratory tract infections

This study compared the in vitro activity of ertapenem, ceftriaxone, cefepime, ciprofloxacin and amoxicillin-clavulanate against 381 aerobic and facultative bacterial pathogens isolated from 320 patients with acute bacterial exacerbation of chronic bronchitis or community-acquired pneumonia. Streptococcus pneumoniae and Haemophilus influenzae accounted for 54.6% of the isolates. The ertapenem MIC was < or =2 mg/L for 98.4% of isolates and > or =8 mg/L for 1.0% (all methicillin-resistant Staphylococcus aureus). Ertapenem had the most potent activity against Enterobacteriaceae, Moraxella catarrhalis, and methicillin-susceptible S. aureus, and its activity against H. influenzae and H. parainfluenzae, all strains of which were susceptible, was not altered by beta-lactamase production. Only one S. pneumoniae strain, a penicillin-resistant isolate, was resistant to ertapenem. Ertapenem was highly active in vitro against pyogenic bacteria recovered from patients with community-acquired lower respiratory tract infections.

A prospective, randomized, double-blind multicenter comparison of parenteral ertapenem and ceftriaxone for the treatment of hospitalized adults with community-acquired pneumonia

BACKGROUND

Ertapenem is a once-daily parenteral beta-lactam licensed in the United States in November 2001 and in Europe in May 2002.

OBJECTIVE

This study compared the efficacy and safety profiles of ertapenem with those of ceftriaxone for the treatment of hospitalized adult patients with serious community-acquired pneumonia (CAP) requiring parenteral therapy.

METHODS

In this prospective, double-blind (with sponsor blinding), multicenter study, adult patients with CAP were stratified by Pneumonia Severity Index (< or = 3 or > 3) and age (< or = 65 or > 65 years) and randomized (2:1) to receive IV or intramuscular (IM) ertapenem 1 g once daily or IV or IM ceftriaxone 1 g once daily. Investigators could switch patients to an oral antimicrobial agent if clinical improvement was shown after at least 3 days of parenteral therapy.

RESULTS

A total of 364 patients were randomized to treatment: 239 to the ertapenem group and 125 to the ceftriaxone group. Three patients in the ertapenem group and 2 in the ceftriaxone group did not receive study therapy. Of the treated patients, 77.1% (182/236) of patients in the ertapenem group and 75.6% (93/123) in the ceftriaxone group were clinically evaluable. Among clinically evaluable patients, the mean (SD) durations of parenteral and total (parenteral plus optional oral) therapy were 5.5 (2.6) and 11.5 (2.7) days for ertapenem and 5.6 (2.8) and 11.7 (3.0) days for ceftriaxone, respectively. Streptococcus pneumoniae was the most frequently isolated pathogen in both treatment groups. Cure rates were 92.2% for clinically evaluable patients in the ertapenem group and 93.6% for those in the ceftriaxone group (95% CI for the difference, adjusted for stratum, -8.6 to 5.7), fulfilling the criteria for statistical equivalence. At completion of parenteral therapy, 94.7% of patients in the ertapenem group and 95.8% in the ceftriaxone group showed clinical improvement. Infused vein complications (ertapenem, 3.4% [8/236]; ceftriaxone, 7.3% [9/123]) and elevated transaminase levels (ertapenem, 6.3% [13/207]; ceftriaxone, 7.1% [8/113]) were the most common adverse events in both groups.

CONCLUSIONS

In this study of hospitalized adult patients, ertapenem therapy, with an oral switch option, was as effective as ceftriaxone with the same oral switch option for treatment of CAP requiring initial parenteral therapy. The overall safety profiles of the 2 drugs were comparable.

Ceftriaxone: an update of its use in the management of community-acquired and nosocomial infections

Ceftriaxone is a parenteral third-generation cephalosporin with a long elimination half-life which permits once-daily administration. It has good activity against Streptococcus pneumoniae, methicillin-susceptible staphylococci, Haemophilus influenzae, Moraxella catarrhalis and Neisseria spp. Although active against Enterobacteriaceae, the recent spread of derepressed mutants which hyperproduce chromosomal beta-lactamases and extended-spectrum beta-lactamases has diminished the activity of all third-generation cephalosporins against these pathogens necessitating careful attention to sensitivity studies. Extensive data from randomised clinical trials confirm the efficacy of ceftriaxone in serious and difficult-to-treat community-acquired infections including meningitis, pneumonia and nonresponsive acute otitis media. Ceftriaxone also has efficacy in other community-acquired infections including uncomplicated gonorrhoea, acute pyelonephritis and various infections in children. In the nosocomial setting, extensive data also confirm the efficacy of ceftriaxone with or without an aminoglycoside in serious Gram-negative infections, pneumonia, spontaneous bacterial peritonitis and as surgical prophylaxis. Outpatient use of ceftriaxone, either as part of a step-down regimen or parenterally, is a distinguishing feature of the data gathered on the agent over the last decade. The review focuses on new applications of the drug and its use in infections in which the causative pathogens or their resistance patterns have changed over the past decade. Ceftriaxone has a good tolerability profile, the most common events being diarrhoea, nausea, vomiting, candidiasis and rash. Ceftriaxone may cause reversible biliary pseudolithiasis, notably at higher dosages of the drug (>/=2 g/day); however, the incidence of true lithiasis is <0.1%. Injection site discomfort or phlebitis can occur after intramuscular or intravenous administration.

CONCLUSIONS

As a result of its strong activity against S. pneumoniae, ceftriaxone holds an important place, either alone or as part of a combination regimen, in the treatment of invasive pneumococcal infections, including those with reduced beta-lactam susceptibility. Its once-daily administration schedule allows simplification of otherwise complex regimens in a hospital setting and has also contributed to its popularity as a parenteral agent in an ambulatory setting. These properties, together with a well characterised tolerability profile, mean that ceftriaxone is likely to retain its place as an important third-generation cephalosporin in the treatment of serious community-acquired and nosocomial infections.

The new antibiotics

It is easy to become overwhelmed by the amount of information available on the new antibiotics and difficult to keep abreast of the appropriate indications for each of them. For most patients with community-acquired infections, the first-line agent is usually not one of the newer agents, but a standard regimen, or at times, no antibiotic at all. The development of resistance is likely to parallel the extent to which these agents are prescribed. They should be used only when standard treatment fails, when compliance with treatment is a real and serious issue, or when the patient has a real allergic reaction to the standard regimen.

Evidence-based medicine: empiric antibiotic therapy in community-acquired pneumonia

A number of national society guidelines exist for empiric management of community-acquired pneumonia but these are, to a large extent, not evidence-based, but based on clinical experience, in vitro data, pragmatism and common sense. Many randomized controlled trials of antibiotic therapy in community-acquired pneumonia have been conducted, but most of these have been powered to demonstrate equivalent efficacy of new treatments in comparison with conventional antimicrobial therapy. Development of new antibiotics has been driven by the emergence of penicillin-resistant Streptococcus pneumoniae, but so far there is no hard evidence that beta-lactam therapy fails in community-acquired pneumonia, at least with the higher doses of penicillins that are commonly used in hospital practice. Nonetheless, newer antibiotics have been deployed including macrolides and quinolones, and have demonstrated equivalent (and in some cases, marginally improved) efficacy to older antibiotic treatments in randomized control trials. A number of studies have shown that it is possible to stratify patients according to severity of illness, to in-patient or out-patient management protocols. These have been validated and refined.

Severe pneumonia. When and why to hospitalize

Relatively simple objective criteria are now available to predict which patients are at risk for bad outcomes from community-acquired pneumonia. In general, these include older patients and those with certain coexisting illnesses (especially neoplastic disease) or findings of altered mental status, hypotension, severe tachycardia, tachypnea, fever, acidemia, azotemia, hypoxemia, hyperglycemia, anemia, or hyponatremia. The major causes of severe pneumonia are S pneumoniae, H influenzae, and L pneumophila. Less common causes include mixed aerobic and anaerobic mouth flora, as well as M pneumoniae, C pneumoniae, gram-negative bacilli, and S aureus. Specific diagnosis is hampered by a lack of reliable diagnostic tests, but Gram's stain of expectorated sputum and cultures of sputum and blood may occasionally be helpful. Many empirical treatment regimens have been recommended, including those of the American Thoracic Society and the Infectious Diseases Society of America, which are reviewed here. It is hoped that better diagnostic tools will permit future targeting of microbes with narrow-spectrum therapy to diminish the risk of selection of resistant strains with empirical regimens.