Designing malaria surveillance strategies for mobile and migrant populations in Nepal: a mixed-methods study

Abstract

Background: As malaria cases have declined throughout Nepal, imported cases comprise an increasing share of the remaining malaria caseload, yet how to effectively target mobile and migrant populations (MMPs) at greatest risk is not well understood. This formative research aimed to confirm the link between imported and indigenous cases, characterize high-risk MMPs, and identify opportunities to adapt surveillance and intervention strategies to them.

Methods: The study used a mixed-methods approach in three districts in far and mid-western Nepal, including (i) a retrospective analysis of passive surveillance data, (ii) a quantitative health facility-based survey of imported cases and their MMP social contacts recruited by peer-referral, and (iii) focus group (FG) discussions and key informant interviews (KIIs) with a subset of survey participants. Retrospective case data were summarised and the association between monthly indigenous case counts and importation rates in the previous month was investigated using Bayesian spatio-temporal regression models. Quantitative data from structured interviews were summarised to develop profiles of imported cases and MMP contacts, including travel characteristics and malaria knowledge, attitudes and practice. Descriptive statistics of the size of cases' MMP social networks are presented as a measure of potential programme reach. To explore opportunities and barriers for targeted malaria surveillance, data from FGs and KIIs were formally analysed using a thematic content analysis approach.

Results: More than half (54.1%) of malaria cases between 2013 and 2016 were classified as imported and there was a positive association between monthly indigenous cases (incidence rate ratio (IRR) 1.02 95% CI 1.01-1.03) and the previous month's case importation rate. High-risk MMPs were identified as predominantly adult male labourers, who travel to malaria endemic areas of India, often lack a basic understanding of malaria transmission and prevention, rarely use ITNs while travelling and tend not to seek treatment when ill or prefer informal private providers. Important obstacles were identified to accessing Nepali MMPs at border crossings and at workplaces within India. However, strong social connectivity during travel and while in India, as well as return to Nepal for large seasonal festivals, provide opportunities for peer-referral-based and venue-based surveillance and intervention approaches, respectively.

Conclusions: Population mobility and imported malaria cases from India may help to drive local transmission in border areas of far and mid-western Nepal. Enhanced surveillance targeting high-risk MMP subgroups would improve early malaria diagnosis and treatment, as well as provide a platform for education and intervention campaigns. A combination of community-based approaches is likely necessary to achieve malaria elimination in Nepal.

Keywords: Focus group discussion; Imported malaria cases; Key informants’ interview; Malaria elimination; Mobile migrant populations (MMPs); Nepal.

Conflict of interest statement

The authors declare that they have no any competing interests.

Figures

Fig. 1

Study site districts (Kanchanpur, Kailali and Bardiya) and formal border crossings (black squares) in far-western and mid-western Nepal (inset). Green shaded areas represent tree cover

Fig. 2

Total number of indigenous and imported cases (bars) and respective proportion of Plasmodium falciparum (Pf) cases (lines) in the three study districts between 2013 and 2016. While the number of indigenous falciparum cases fell in 2014, corresponding with a spike in the use of RDTs, the proportion of imported falciparum cases was stable

Fig. 3

All species imported and indigenous annual parasite index (API) at the village development committee (VDC) level in the three study districts between 2013 and 2016. Areas of higher transmission are located in the south of Kailali bordering Bardiya National Park and on the northern border with Kanchanpur. VDCs that are predominantly covered by a national forest with very low populations are shaded green

Fig. 4

Indigenous annual parasite index (API) of Plasmodium vivax and P. falciparum at the village development committee (VDC) level in the three study districts between 2013 and 2016. National forests are shaded green

Fig. 5

Destinations, travel routes and key transit points of 138 trips to India reported by 137 imported cases and MMP peers (Table 4), overlaid onto a map of predicted Plasmodium vivax all ages prevalence rate [44]

Fig. 6

MMP peer network statistics of imported cases recruited in Kailali, Kanchanpur and Bardiya and reporting travel to India