Do mosquito coils prevent malaria? A systematic review of trials

Official guidelines commonly advise travelers to burn mosquito coils as one means of preventing malaria. The objective of this study was to discover if insecticide-containing mosquito coils (1) prevent mosquito bites and therefore malaria acquisition, and (2) are safe in terms of their adverse effects on human users.

We sought published and unpublished controlled trials in this area, by (1) contacting experts, (2) searching the Cochrane Library, (3) interrogating bibliographic databases, (4) Internet search, (5) citation scanning, (6) scanning conference proceedings, and (7) writing to manufacturers.

Fifteen controlled trials of insecticide-containing mosquito coils met our predefined inclusion criteria. We found no controlled trials measuring the incidence of clinical malaria as an outcome. Studies tested the efficacy of coils in achieving mosquito bite reduction (reported in 14 studies), mosquito repellence (seven), deterrence (five), "knockdown" effect (five), and percentage mosquito mortality (seven). Of the 38 separate outcome measures reported, antimosquito efficacy was reported as positive for >95%. One trial reported no antimosquito effect at all, for one outcome only. Some insecticide classes and strengths were associated with better antimosquito outcomes than others. One trial identified possible adverse effects (irritation of the eyes and nose) in human users of this technology.

There is no evidence that burning insecticide-containing mosquito coils prevents malaria acquisition. A randomized field trial should be conducted, with malaria incidence as a primary outcome. There is consistent evidence that burning coils inhibits nuisance biting by various mosquito species. The potential harmful effects of coil smoke on human users should be investigated.