Upper respiratory tract infection and serum antibody responses in nursing home patients

Residents of a Veterans Administration nursing home care unit (NHCU) were observed for the development of upper respiratory tract infection (URI) during 12 consecutive months to determine the frequency of sporadic cases of outbreaks of URI and to characterize them clinically and by laboratory means. Fifty-nine episodes of URI occurred in 56 residents during the study period. Serologic testing or virus isolation proved or suggested an etiologic agent on 22 occasions. URI was more common in late Fall and Winter and was caused by various agents, including influenza, Mycoplasma pneumoniae, respiratory syncytial virus, and parainfluenza viruses. A minor outbreak of influenza B in February 1986 contrasted with previous cases of URI in that the patients had a higher mean temperature and abnormal breath sounds, and they were clinically sicker. This suggests that clinical and epidemiologic surveillance during the influenza season may allow the early recognition of influenza in elderly nursing home residents. Over a 4-year period 147 serum antibody responses after influenza infection or influenza vaccination were compiled. Antibody responses to individual influenza vaccine components were measured 75 to 90 days after vaccination. The geometric mean titer (GMT) and the percentage of samples with antibody levels ⩾ 1:40 were determined for each of the three antigenic subtypes on 3 consecutive years. The GMT to individual vaccine components was consistently greater than 1:40, except to influenza B/Singapore in 1984 and A/Chile and B/U.S.S.R. in 1985, when these subtypes were first included in the vaccine, suggesting the NHCU residents responded less vigorously to unfamiliar vaccine subtypes. In 1984 the GMT to A/Phillippines of unvaccinated NHCU residents without URI was surprisingly no different from the corresponding GMT of their vaccinated counterparts, raising the possibility that an influenza A/Phillippines outbreak in 1983 conferred herd immunity.