Rationale:

• Because no chemoprophylactic regimen is 100% effective, measures should be taken to reduce vector exposure.

Evidence:

• Of 799 patients with imported malaria with onset of illness in 2002 and for whom prophylaxis information was available, 21% took a CDC-recommended drug for the area of travel, indicating that chemoprophylaxis regimens are not 100% effective and that measures should be taken to reduce mosquito exposure as well (22).
• One questionnaire-based survey of 89,617 European tourists returning from East Africa found that the incidence of malaria was significantly reduced by sleeping in an air-conditioned room (P=0.04) and wearing long-sleeved shirts and trousers (P=0.02) (31).
• A systematic review of 18 randomized, controlled trials in malaria-endemic settings (involving nontravelers) found that nets impregnated or sprayed with permethrin reduced the number of mild malaria episodes (absolute risk reduction 39%; 27% to 48%) and child mortality (relative risk of death, 0.83; 0.77 to 0.90) compared with no nets or untreated nets (32).
• A community-based, randomized, controlled trial in an area of intense perennial transmission in western Kenya showed that permethrin-treated bed nets reduced P. falciparum transmission by 90%. Bed net efficacy (as measured by percent reduction in Anopheles gambiae feeding) declined with increasing number of days since previous insecticide application, as follows: <90 days, 82%; 90 to 180 days, 63%; >180 days, 17% (33).
• A case-control study (96 cases, 613 controls) showed that the use of insect repellant soap (containing 20% DEET, 0.5% permethrin) reduced the risk of malaria by 92% in an Afghan population also using insecticide-treated bed nets (adjusted OR, 0.08 [CI, 0.01 to 0.61]; P=0.001) (34).
• A cluster-randomized, placebo-controlled trial involving 127 Afghan refugee families showed that the use of insect repellant soap (containing 20% DEET, 0.5% permethrin) reduced the risk of P. falciparum malaria by 56% over 6 months of follow-up (OR, 0.44 [CI, 0.25 to 0.76]; P=0.004) (35).
• A small nonrandomized, controlled trial in eight U.S. Air Force recruits found that permethrin-treated uniforms significantly reduced the risk of mosquito bites over 8 hours (relative risk reduction, 93% [P<0.01]). The topical application of DEET further reduced the risk of mosquito bites (relative risk reduction, 99.9% [P<0.01]) (36).
• Although one study did not associate the use of a commercially available insecticide with malaria protection (P>0.2) (31); one randomized, controlled trial involving eight people showed that insect repellent soap (20% DEET, 0.5% permethrin) reduced the number of sand fly bites for up to 8 hours (P<0.05) (37).

Comments:

• Travelers taking chemoprophylaxis frequently have a false sense of security, leading them to ignore mosquito repellent measures. A survey of North American and European travelers returning from Africa found that although 95% used chemoprophylaxis, only 62% used both chemoprophylaxis and two or more antimosquito measures (38).
• Products containing ~30% DEET are considered safe and effective for 4 to 6 hours in adults and children older than 2 months, if used according to the manufacturer's directions. A useful list of products and manufacturer contact information has been compiled (39). Instructions on the appropriate application of DEET products are provided by the EPA.
• Products containing niacin, citronella, and other plant and animal oils provide little if any protection. Some perfumed products may attract mosquitoes.
• Bed nets should be treated with permethrin (300 to 500 mg/m²) every 6 months to maintain effectiveness (40). Permethrin-treated clothing and nets are safe for pregnant women and children. Bed nets should be properly tucked under the mattress to prevent access by mosquitoes.