Epidemiology of intracellular pathogens

Abstract

Epidemiologic studies of Chlamydia pneumoniae have been conducted throughout the world. A rate of antibody prevalence of approximately 50% has been found in adults, with small regional differences. We studied the antibody prevalence of C. pneumoniae in healthy persons and patients with acute respiratory infections in Japan. The microplate immunofluorescence antibody (MFA) technique was used for measuring antibodies, and the cases with IgG titers of greater-than-or-equal 1:64 were considered to have had past chlamydial exposure. Using this criterion, positive serum antibodies against C. pneumoniae were found in 67.4% of healthy subjects and 74.2% of adult patients with respiratory infections. Some seroepidemiologic studies in Western countries have shown that epidemics of C. pneumoniae respiratory infections occur in a 4--6-year cycle, like a Mycoplasma pneumoniae infection. However, during our 7-year survey from 1988 to 1994, we were not able to observe any epidemic episodes. The prevalence of the antibody was lower than 10% in children 5 years old or younger. It increased rapidly between ages 6 and 15, reaching a plateau of 60%. Results suggest that in Japan a high infection rate might occur in children at nursery schools, kindergartens and elementary schools. We encountered an outbreak of C. pneumoniae infection and we were able to trace the source of the infection to a family and the spread of the infection to the schools which the children attended. Transmission is of the non-vector type. The incubation period is 3 to 4 weeks. Transmission occurs only after repeated and close contacts. Small outbreaks may occur in households and schools where persons have prolonged close contacts. Unlike acute viral infections, it may spread slowly.