Cohort Study on the Recurrence Rate of High Altitude Pulmonary Oedema.

Keeping in view the importance of High Altitude Pulmonary Oedema (HAPO) as well as the absence of published evidence as regards recurrence rate of this disease, a cohort study was undertaken, based on data available with the Central Diseases Registry. The inception cohort consisted of all cases of HAPO occurring over a one year period, This cohort was followed up for another 12 months, to observe any recurrence. The study revealed that the recurrence rate of HAPO in terms of Incidence density was 1.83 per 1000 person-months of those who had an initial episode (95% confidence limit 0.53 to 3.13 per 1000 person-months). The cumulative incidence was 32.9 per 1000, over an average follow up of 18 months (95% confidence limit 4.55 to 61.25 per 1000). The time gap between the initial episode and recurrence was 115 to 208 days. All recurrent cases had their initial as well as recurrent episode at the first stage of high altitude (9000 to 12000 feet), with the onset being within 48 hours of entry into high altitude. Based on the findings, some recommendations for prevention of recurrence of HAPO have been submitted.