Cluster of Haemophilus influenzae type b infections in adults

Haemophilus influenzae type b commonly causes illness in young children, among whom transmission is known to occur. Most adults are believed to be immune to H influenzae type b and outbreaks of disease among adults appear to be uncommon. From July 14 to Aug 12, 1985, a cluster of six cases of acute febrile illness with cultures positive for H influenzae, biotype II (five cases) or untyped H influenzae (one case), occurred among adults in a nursing home and an adjoining hospital. All six case-patients had personal contact with at least one other case-patient. Among the 46 nursing home residents, men were more likely than women to become ill (44% vs 0%). This cluster of disease suggests that elderly adults may be more susceptible to H influenzae infection than is generally recognized and that outbreaks among adults may result from person-to-person transmission.