NESTED CASE - CONTROL ANALYSIS OF THE RISK FACTORS FOR HIGH ALTITUDE PULMONARY OEDEMA.

A nested case-control study was undertaken on a cohort of soldiers inducted into high altitude area (11000 to 16000 feet) of Western Himalayas, with the objectives of studying the incidence of high altitude pulmonary oedema (HAPO) and its association with physical exertion and certain other predetermined risk factors. The study indicated that the cumulative incidence of HAPO was 1.42 per 1000 inductions. The association with moderate/strenuous physical exertion within 24 hours of entry into high altitude was significant (Odds ratio (OR) = 3.19; 95% confidence limits (CL) = 1.23 to 8.15); however, this association was not significant for the period 24 to 48 hours or > 48 hours. Physical exertion during first 24 hours was also significantly associated with severity of disease (OR = 14.67, 95% CL = 3.61 to 64.04), but not after 24 hours. Previous history of "high altitude sickness" was also significantly associated with HAPO (OR = 2.74, 95% CL = 1.12 to 6.77). Physical exertion during first 24 hours was found to carry an attributable risk of 2.56 per 1000 inductions and an etiologic fraction of 17.8%. No significant association of HAPO was observed with age, type of inductee (fresh/reinductee), native place, alcohol consumption and smoking.