Seroepidemiological evidence of infectious diseases in United States marine corps personnel, Okinawa, Japan, 1975-1976

Leptospira spp., Rickettsia tsutsugamushi, and Japanese encephalitis virus have been important causes of illness and infection among US military personnel stationed in endemic areas of Japan, Korea, the Philippines, Taiwan, and Vietnam. US Marines stationed in Okinawa, Japan, receive training which exposes them to infection with these etiologic agents and other arthropod-borne viruses during field exercises in endemic foci of Southeast Asia. The objectives of this study were to determine the relative important of these infectious agents among US Marines in Okinawa, Japan, and to estimate the infection rates of each. The basis of the study was a serological survey with repeat bleedings after one year. None of the 507 marines who were bled for a second time in 1976 had serological evidence of infection with Japanese encephalitis virus, Chikungunya virus, swine influenza virus (A/New Jersey/76), or Rickettsia mooseri. A single infection (0.2%) was attributed to Leptospira sp., as evidenced by a seroconversion from antibody negative to antibody positive. Rickettsia tsutsugamushi was responsible for six infections (1.2%) among the 507 subjects. The recent epidemic strain of influenza virus, A/Victoria/75, infected at least 53 of 411 subjects tested (13%), while B/Hong Kong/72 caused at least 26 infections (6%). In addition to those subjects who developed diagnostic rises in antibody titer to influenza viruses, others were probably infected but failed to show fourfold rises. This is evidenced by the statistically significant differences between prevalence of antibody titers ≥ 1:20 to two influenza viruses in 1975 and 1976. A table shows the prevalence and geometric means titers (GMT) of antibody to influenza viruses during 1975 and 1976. The prevalences and GMTs of antibody to A/Victoria/75 and B/Hong Kong/72 were greater in 1976 than in 1975 (p<0.01).