Determinants of sickness in marine recruits.

Abstract

Is the human environment, as expressed by social and cultural attributes of defined groups, a more potent determinant of sickness than the conventionally attributed single causes like microorganisms, individual disposition and proneness to accident or exposure to its risk? These two alternatives can be tested in Marine recruits where the defined, face-to-face group is the platoon, isolated from other platoons but otherwise highly comparable. Sickness in the platoon was indexed by the number of sick calls and each sick call was categorized by the supervising personnel into: a) infectious, b) skin, c) other non-traumatic, d) musculo-skeletal or traumatic, and e) unspecified complaints. Under the single-cause-single-effect hypothesis, differences in amount of sickness between platoons are explained by introductions of infectious diseases or by differences in the drill procedure leading to differential sickness rates of the musculo-skeletal and trauma complaint type. Thus, this hypothesis predicts that in a given platoon a high sickness rate of one complaint type is unlikely to be accompanied by a high rate of another complaint type, unless the two single causes involved both happen to act excessively on the same platoon. Likewise, the hypothesis predicts that the time of peak sick call incidence for one complaint type is unlikely to coincide with the time of peak incidence for another complaint type. The alternative hypothesis—that the cause of increase of a sickness in a recruit group is largely nonspecific—predicts an association between the sick call rates of various complaint types in the same platoon, and a similarity of training stages having peak sick call incidences of the various complaint types. A similar reasoning holds for the time of peak incidence of sickness comparing one platoon with another. In each platoon the respective percentages of sick calls where the recruit was ordered to be admitted to the hospital, to have no duty, to have light duty, or to go back to full duty were essentially similar, and this similarity in relative distributions of recruit disposal was also observed when comparing the various stages of training. This supports the contention that in this study the number of sick calls per platoon is a valid index of sickness in the platoon. A three-way analysis of variance of the number of sick calls per platoon was performed and the main effects due to complaint type, platoon, and stage of training were assessed, as well as their first-order interactions. For all complaint types, the maximum number of sick calls in most of the platoons occurred during the second and third week of training and the minimum number during the sixth and seventh week. The training-stage by complaint-type interaction was small compared to the main effects themselves. In addition, there was a significant main effect due to platoons, whereas the platoon by complaint-type and the platoon by training-stage interactions were small. These findings contradict the single-cause-single-effect and support the alternative hypothesis. The analysis of variance of platoon sickness, as indicated by number of sick calls, provides a test for the two competing hypotheses of causation.