Measuring the physical and economic impact of filarial lymphoedema in Chikwawa district, Malawi: a case-control study

BACKGROUND Lymphatic filariasis (LF) is one of the primary causes of lymphoedema in sub-Saharan Africa, and has a significant impact on the quality of life (QoL) of those affected. In this paper we assess the relative impact of lymphoedema on mobility and income in Chikwawa district, Malawi. METHODS A random sample of 31 people with lymphoedema and 31 matched controls completed a QoL questionnaire from which both an overall and a mobility-specific score were calculated. Two mobility tests were undertaken, namely the 10 m walking test [10MWT] and timed up and go [TUG] test, and a subset of 10 cases-control pairs wore GPS data loggers for 3 weeks to measure their mobility in a more natural setting. Retrospective economic data was collected from all 31 case-control pairs, and each participant undertaking the GPS activity recorded daily earnings and health expenditure throughout the observation period. RESULTS Cases had a significantly poorer overall QoL (cases = 32.2, controls = 6.0, P < 0.01) and mobility-specific (cases = 43.1, controls = 7.4, P < 0.01) scores in comparison to controls. Cases were also significantly slower (P < 0.01) at completing the timed mobility tests, e.g. mean 10MWT speed of 0.83 m/s in comparison to 1.10 m/s for controls. An inconsistent relationship was observed between mobility-specific QoL scores and the timed test results for cases (10MWT correlation = -0.06, 95% CI = (-0.41, 0.30)), indicating that their perceived disability differed from their measured disability, whereas the results were consistent for controls (10MWT correlation = -0.61, 95% CI = (-0.79, -0.34)). GPS summaries indicated that cases generally walk shorter distances at slower speeds than control, covering a smaller geographical area (median area by kernel smoothing: cases = 1.25 km2, controls = 2.10 km2, P = 0.16). Cases reported earning less than half that earned by controls per week (cases = $0.70, controls = $1.86, P = 0.064), with a smaller proportion of their earnings (16% vs 22%, P = 0.461) being spent on healthcare. CONCLUSIONS Those affected by lymphoedema are at a clear disadvantage to their unaffected peers, experiencing a lower QoL as confirmed by both subjective and objective mobility measures, and lower income. This study also indicates that objective measures of mobility may be a useful supplement to self-assessed QoL questionnaires when assessing the future impact of lymphoedema management interventions.