Maximizing the use of human population movement data for malaria control and elimination

Abstract

Malaria transmission through human population movement (HPM) poses a major obstacle to malaria elimination. I hypothesize that the collection of routine surveillance data on travel patterns of people with malaria in a country nearing malaria elimination could be used to maximize the use of HPM data for malaria control and elimination. From May 2017 to December 2021, 6320 malaria patients were enrolled in 107 health facilities Lao PDR. Information was obtained on demographics, travel patterns and mobile phone use and ownership. Dried blood spots were collected to examine malaria parasite DNA. 27% were females and 73% males, with a median age of 19 years. 58% had P. vivax, 40% P. falciparum, 1% mixed P. falciparum and P. vivax, 0.02% P. knowlesi and 0.02% P. ovale. The proportion of malaria patients travelling increased from 55% in 2017 to 85% in 2021, despite COVID restrictions. Travel to the forest was most common, increasing from 53% to 75%. Attapeu was the most popular destination for inter-province travel (44-100%). During COVID, travel concentrated to Attapeu (from 46% to 60%) and Phouvong (from 26% to 53%), while inter-province and inter-district travel elsewhere decreased. The demographics of forest visitors remained unchanged. Males aged 25–49 years comprised the largest proportion of forest visitors and farmers remained the most popular occupation

(59-69%). Among reasons for visiting the forest, collecting forest products became less popular (from 36% to 24%) while cutting trees or wood became the most popular (from 17% to 35%). Visitors tended to stay overnight in the forest (71%). Trips to the forest were less frequent but involved longer overnight stays during COVID. During the 2020- 2021 malaria outbreak in Attapeu province, the ratio of P. falciparum to P. vivax species increased during the epidemic (from 0% to 100% P. falciparum). The outbreak strains (LAA1, LAA2 and LAA7) were found in Phouvong, Xanxay and Xaysettha districts. The demographic distribution of those carrying the outbreak strain was mainly similar to those not carrying the strain, with slight differences in age and gender, but no differences in occupation. Timing of the rainy season and volume of rainfall did not differ from other years suggesting climate did not contribute to causing the outbreak. Phouvong was an overwhelmingly popular destination for travel from other districts (93% of trips), especially to the forest (86% of trips). Genetic distance was 0 between parasites in all blood samples from people who travelled except for one, suggesting a localized outbreak with recent proliferation of outbreak strains. While mobile phone use in the general population was high according to the census, 24% of malaria patients owned or used a mobile phone. At district level, API was weakly negatively correlated with mobile ownership (R2= 0.3, p= 0.005). Mobile phone ownership and use were significantly lower when compared to the general population (p<0.001), regardless of province, gender separated by province, age group and age groups separated by gender (p<0.001). In conclusion, routine collection of detailed travel surveys from people with malaria provided rich information to inform activities and future plans for the national malaria programme. Low mobile phone ownership among malaria cases suggests use of cell phone data to analyse travel patterns will be relatively uninformative and travel surveys should be prioritised.