Incidence of community-acquired pneumonia requiring hospitalization. Results of a population-based active surveillance Study in Ohio. The Community-Based Pneumonia Incidence Study Group.

BACKGROUND: Pneumonia is the leading cause of death due to infectious diseases in the United States; however, the incidence of most infections causing community-acquired pneumonia in adults is not well defined. METHODS: We evaluated all adults, residing in 2 counties in Ohio, who were hospitalized in 1991 because of community-acquired pneumonia. Information about risk factors, symptoms, and outcome was collected through interview and medical chart review. Serum samples were collected from consenting individuals during the acute and convalescent phases, and specific etiologic diagnoses were assigned based on results of bacteriologic and immunologic tests. RESULTS: The incidence of community-acquired pneumonia requiring hospitalization in the study counties in 1991 was 266.8 per 100,000 population; the overall case-fatality rate was 8.8%. Pneumonia incidence was higher among blacks than whites (337.7/100,000 vs 253.9/ 100,000; P < .001), was higher among males than females (291.4 vs 244.8; P < .001), and increased with age (91.6/100,000 for persons aged < 45 years, 277.2/ 100,000 for persons aged 45-64 years, and 1012.3/ 100,000 for persons aged > or = 65 years; P < .001). Extrapolation from study incidence data showed the projected annual number of cases of community-acquired pneumonia requiring hospitalization in the United States to be 485,000. These data provide previously unavailable estimates of the annual number of cases that are due to Legionella species (8000-18,000), Mycoplasma pneumoniae (18,700-108,000), and Chlamydia pneumoniae (5890-49,700). CONCLUSIONS: These data provide information about the importance of community-acquired pneumonia and the relative and overall impact of specific causes of pneumonia. The study provides a basis for choosing optimal empiric pneumonia therapy, and allows interventions for prevention of pneumonia to be targeted at groups at greatest risk for serious illness and death.

Susceptibility of ninety-eight clinical isolates of Legionella to macrolides and quinolones using the Etest.

Isolates of Legionella from 98 patients with Legionnaires' disease hospitalized in Columbus, Ohio, USA between 1991 through 1995 were tested for antimicrobial susceptibility to macrolides and quinolones using the Etest. Most (87%) isolates were Legionella pneumophila serogroup 1. All isolates tested remain susceptible to erythromycin, azithromycin, clarithromycin, ciprofloxacin, ofloxacin, and levofloxacin. In vitro susceptibility testing of Legionella to representative macrolides and quinolones should be considered to detect the emergence of resistant isolates.

Stability of Legionella urinary antigens over time.

Twenty-two urine samples positive for Legionella pneumophila serogroup 1 antigen by EQUATE radioimmunoassay (RIA) (Binax, Portland, ME, USA) were stored at various temperatures and the RIA repeated at 1, 7, 30, 90, and 120 days to evaluate stability of the urinary antigens. The mean ratios of patient/negative control remained stable. Although there was a 10% decrease in the mean ratios after 1 month, changes were not significant. However, individual samples with ratios close to 3 may fall to < 3.

Comparison of Binax Legionella Urinary Antigen EIA kit with Binax RIA Urinary Antigen kit for detection of Legionella pneumophila serogroup 1 antigen.

The Legionella Urinary Antigen EIA kit (Binax, Portland, Maine) was compared with the EQUATE RIA Legionella Urinary Antigen kit (Binax) for its ability to detect the presence of urinary antigens to Legionella pneumophila serogroup 1. Urine specimens from patients without Legionnaires' disease (n = 33) were negative by both methods (specificity, 100%). Twenty (77%) of 26 urine specimens from patients with Legionnaires' disease positive by the radioimmunoassay kit were also positive by the enzyme immunoassay (EIA) kit. If the cutoff for a positive EIA result were lowered to a ration of > or = 2.5, 23 of 26 (88%) urine specimens would have been positive by EIA and the specificity would remain 100%. Use of the EIA kit is an acceptable method for detecting L. pneumophila serogroup 1 urinary antigens by laboratories that do not want to handle radioactive materials.

Reevaluation of the definition of Legionnaires' disease: use of the urinary antigen assay. Community Based Pneumonia Incidence Study Group.

Cases of Legionnaires' disease have been categorized as definitive and presumptive. The sensitivity and specificity of antibody titers of > or = 256 and of urinary antigen ratios of > or = 3 were evaluated in 68 patients with "definitive" Legionnaires' disease and in 636 patients with pneumonia who had negative cultures and did not have fourfold rises in titers of antibody to Legionella pneumophila. An acute-phase antibody titer of > or = 256 did not discriminate between cases and noncases (10% vs. 6%; P = .29). The urinary antigen assay gave a positive result in fewer than 1% of noncases but was positive in 55.9% of all cases. This assay was most sensitive (80%) in cases in which L. pneumophila serogroup 1 was isolated. We propose that the case definition for definitive Legionnaires' disease be expanded to include positive urinary antigen assays and that the category of presumptive Legionnaires' disease--based on acute-phase or standing antibody titers of > or = 256 in the nonoutbreak setting--be discarded. The urinary antigen assay will be a valuable tool in the prompt diagnosis of Legionnaires' disease.