The epidemiology of malaria in the Papua New Guinea highlands: 4. Enga Province.

Of all Papua New Guinea provinces, Enga has the largest proportion of people living at altitudes that preclude malaria transmission. However, the first systematic surveys in 1979 showed that malaria was endemic in lower-lying valleys to the north and east of the province. A series of new surveys conducted in both wet and dry seasons showed that these areas remain the main malaria focus in Enga. However, over the last 25 years the risk of malarial infections has increased substantially in areas < 1200 m (from 10% to 37-41%). In these low-lying areas people acquire substantial antimalarial immunity and most infections are asymptomatic. However, people in villages in these areas had significantly lower mean haemoglobin levels (13.0 vs 14.0 g/dl, p < 0.001) than in areas above 1200 m, where overall prevalence rates (0-9%) have not changed much. In areas between 1200 and 1600 m epidemics with parasite prevalence rates in excess of 20% have been found to occur. Malaria was a significant cause of febrile illness only in endemic areas or during outbreaks. Although rarely used, sleeping under a bednet was associated with a significant reduction in risk of malaria infection (adjusted OR = 0.45, p = 0.01). On the other hand, sleeping in garden houses away from the main villages increased the risk of malaria infection (adjusted OR = 1.6, p = 0.03). Malaria control in outlying, malarious areas of Enga province could therefore be based on the distribution of long-lasting impregnated bednets, while at the same time addressing the additional risks posed by the high mobility of many of these populations through targeted health education.