NOSOCOMIAL TRANSMISSION OF DISEASE CAUSED BY NONTYPABLE STRAINS OF HAEMOPHILUS-INFLUENZAE

Purpose: The authors evaluated a geographic and temporal cluster of lo wer respiratory tract infections due to unencapsulated (serologically nontypeable) Haemophilus influenzae to determine whether this event re presented the transmission of a single clone. Methods and materials: H influenzae was recovered from eight patients at a nursing home and fr om three patients in an adjacent acute care hospital. Serotypes, bioty pes, outer membrane protein profiles, and multilocus enzyme genotypes were determined to characterize bacterial isolates. Patient records we re retrospectively examined to determine clinical and epidemiologic ch aracteristics. Results: During a 10-day period in September 1991, lowe r respiratory tract infections caused by H influenzae were diagnosed i n four patients residing in a single nursing home unit. Oropharyngeal cultures from four of seven asymptomatic roommates of these patients a lso grew H influenzae. During the month before and after the nursing h ome cluster of cases, four other individuals in acute care areas of th e hospital had positive sputum cultures for H influenzae. Three of the se latter specimens were also available for analysis. All H influenzae isolates were unencapsulated and beta-lactamase-neqative. Eight of th e nine isolates from the nursing home patients (two morphologically di stinct colony types of H influenzae were isolated from one case) had a single outer membrane protein profile arbitrarily designated as X and a single multilocus enzyme genotype arbitrarily designated as A. In c ontrast, none of the isolates from the acute care cases had this profi le (P less than or equal to 0.02; two-tailed Fisher's exact test). The isolates obtained from two of the patients in acute care areas had an outer membrane protein profile arbitrarily designated as Y and a sing le multilocus enzyme genotype designated as B. These two patients were contemporaneously hospitalized in adjacent intensive care unit cubicl es. The remaining isolates displayed an outer membrane protein profile arbitrarily designated as W. All roommates of the four patients in th e nursing home were administered oral rifampin 600 mg daily for 4 days . H influenzae was not recovered from follow-up oropharyngeal cultures obtained 1 week after the completion of therapy. No beta-lactamase-ne gative H influenzae were identified in this unit during the subsequent 9 months. Conclusion: This study furnishes strong evidence for the no socomial transmission of a clone of unencapsulated H influenzae in a n ursing home unit. Epidemiologic data showed temporal and geographic cl ustering of respiratory tract infections and colonization by H influen zae. Outer membrane protein profiles and multilocus enzyme genotype an alysis indicated that seven of eight patients at the nursing home carr ied a single clone of unencapsulated H influenzae. Laboratory and epid emiologic data also demonstrated the presence, and possible nosocomial transmission, of a second clone of unencapsulated H influenzae in a p hysically separate area of the hospital. Finally, although a causal re lationship is not proven, the outbreak ended following the administrat ion of rifampin prophylaxis of asymptomatic carriers.