The incidence of malaria among European and North American travellers returning from Africa has increased markedly during the past decade (1, 2). (a) Especially significant is the rise of malaria incidence among travellers to Kenya, which receives more than 400 000 travellers from Europe and North America each year. (b) The number of Plasmodium falciparum infections acquired in Kenya and imported into the United Kingdom and the USA tripled between 1977 and 1986 (1). (a) The increased number of travellers to Kenya, and the lack of effective and safe chemoprophylactic regimens, contributed to the increased number of cases. The lack of optimal chemoprophylaxis has led to an increased risk for acquiring malaria during travel (3).
The lack of highly safe and effective drugs to prevent infection with chloroquine-resistant P. falciparum has created a dilemma for travellers and for those who develop recommendations for malaria prevention. In North America and Europe, at least sixteen different drug regimens are recommended by various authorities for travellers to East Africa (4-6). Because many chemoprophylactic regimens do not eliminate the risk for infection, many experts recommend that travellers carry a curative dose of a drug. This dose is to be used to treat a febrile illness, when medical care is not available, in an effort to prevent death from P. falciparum infection. In addition to chemoprophylaxis, antimosquito measures, such as repellents and mosquito nets, are frequently recommended because they are considered safe and effective ways of reducing mosquito contact (7).
To formulate malaria prevention recommendations for travellers and to evaluate the use and efficacy of these measures, it is necessary to determine which measures are used and to assess the risk for malaria among travellers (8). The lack of consistent recommendations is understandable because such information is not available to travellers from most countries. A cohort of travellers departing from Kenya was therefore surveyed, in order to determine the use of and compliance with measures to prevent malaria, to assess the frequency of self-treatment for episodes of presumed malaria during travel, and to determine the occurrence of adverse reactions to antimalrial drugs as well as of episodes of malaria during and after travel in Kenya.
Materials and methods
A questionnaire, available in four languages (English, French, German, and Italian), was administered to travellers departing from Nairobi airport for Europe on all scheduled flights between 1 and 21 September 1987. The questionnaire was distributed and collected before boarding. Data collected concerned the duration and purpose of travel, countries and areas visited within Kenya, preventive anti-malarial measures used, adverse drug reactions experienced, and episodes of suspected or confirmed malaria. Eight to ten weeks later a follow-up questionnaire was mailed to these travellers. The follow-up questionnaire asked about compliance with prophylaxis and about malaria episodes after leaving Kenya. To determine the non-response bias, a random sample of travellers from North America and the United Kingdom who did not return the second questionnaire were contacted and interviewed by telephone. All cases of malaria diagnosed by a physician and all cases of persons hospitalized because of adverse reactions to malaria drugs were investigated by contacting the physician who had treated the patient. The diagnosis of malaria was considered verified if a record was available of a blood-smear examination that indicated the presence of Plasmodium parasites.
Compliance with chemoprophylaxis was defined as the regular, uninterrupted use of prophylactic drugs during travel in Africa and for four or more weeks after leaving. Use of adequate antimosquito measures was defined as the use of two or more such measures (bed nets, insect repellents, protective clothing at night, insecticides, staying indoors at night). …