A clinical and epidemiologic study of Q fever was conducted in the Eastern province of Saudi Arabia which indicates that patent infection is not uncommon among Americans residing in the oil production area, but probably is exceptional among the Saudi population. Skin tests performed on long-term American residents revealed a 15% frequency of positive reactions; skin tests performed on a control population of transit American military personnel were all negative. A skin test and serological survey carried out on a larger group of Saudi subjects provided evidence of widespread and prevalent subclinical infection. Among Saudis, skin test reactivity increased with age, was significantly greater in frequency among males than among females, at any age, and attained the highest frequency in the 30- to 39-year age group. With the sensitive radioisotope precipitation test, 70% of sera from adult Saudis was significantly reactive. A small number of Saudis studied with the skin test, the capillary agglutination test and the radioisotope precipitation test were all found to be reactive with one or more tests. There was no apparent correlation between skin test reactivity to Q fever antigen and Brucella antigen among a small group of Saudi subjects. Serological tests on milk samples from cattle, and on sera from sheep and goats have provided evidence that Q fever is present in domestic animals, and that animals imported into Saudi Arabia from an area free of Q fever soon acquire the infection.
Clinical infection among foreign residents of Saudi Arabia appears to be frequently accompanied by evidence of mild hepatic dysfunction, which is in accordance with a number of published reports on clinical manifestations. The literature dealing with the complications of clinical Q fever which may be of epidemiological significance has been cited and discussed, and contemporary views on the importance of subclinical infection in man have been considered in detail.
It can be concluded that Q fever is holoendemic among the indigenous population of Eastern Saudi Arabia, that subclinical infection develops in childhood and that practically all young adults have had sensitizing contact with the infectious agent. Among rural Saudis infection is most likely to occur through intimate contact with large domestic animals, by the consumption of raw milk from infected animals, and by inhalation of infectious material. Foreign residents, having no close contact with livestock and consuming only pasteurized milk, are most likely to acquire infection through the inhalation of infected dust or aerosols. Ethnic and age differences in host-susceptibility may play an important role in the differing expression of infection among Saudis and Americans; these possibilities have yet to be explored.
Chief of Internal Medicine, Medical Department, Arabian American Oil Company, Dhahran, Saudi Arabia.