In endemic areas, malaria is a major health burden for employees of international companies, including expatriates and other non-immune workers. During the construction of the 1,000 km-pipeline from Chad oilfields to the coast of Cameroon, up to 18.5% of workers suffered from malaria 12 months after the start of construction . Malaria was also the main health issue among employees of an oil palm plantation . Other examples of expatriates from non-endemic areas working in malaria-endemic areas are members of the Red Cross or other humanitarian NGOs, employees of private companies, including stopover crews, employees of governmental and international organizations and military personnel, all of whom represent non-immune travellers.
Resistance of P. falciparum to most anti-malarial drugs makes the appropriate use of AVPMs even more important. Few studies have assessed compliance with AVPMs. Compliance has mostly been studied as a secondary outcome in the context of assessment of compliance with chemoprophylaxis [4, 5, 7, 9, 11, 22]. In the present study, which was conducted in a large sample of professional travellers, compliance with wearing long clothing at night, using IIBNs and using insect repellents was the primary outcome.
The prevalences of "correct" compliance with wearing long clothing and the use of IIBNs were more than 2.5 times higher than the prevalence of "correct" compliance with the use of insect repellents. The need for repeated applications of repellents could explain this difference from other AVPMs. Moreover, the social and staff pressures to be compliant with visible measures (i.e., wearing long clothing and using IIBNs) may be higher than the pressure to comply with non-visible measures, such as the use of repellents.
Absence of competing compliance
Some studies have shown no association  or even competition  between the use of malaria prophylactic measures. In the present study, there was no competing compliance between the three AVPMs. "Correct" compliance with one out of the three AVPMs was associated with "correct" compliance with one or two of the other AVPMs in bivariate or in multivariate analyses. Moreover, there was a significant association between "correct" compliance with any AVPM and the reported "correct" compliance with chemoprophylaxis with a dose-effect relationship (i.e., having good compliance with chemoprophylaxis increased the odds of having "correct" compliance with AVPMs). These findings are in agreement with previous reports [12, 17, 23] that suggest common pathways for prophylactic behaviours.
In a French cohort of 899 travellers , age over 50 years was associated with poor AVPM compliance. In the present study, age over 24 years, being a staff member and the occurrence of a life event during the stay were associated with "correct" compliance with one or several AVPMs. These individual factors associated with "correct" compliance could be explained by increased maturity, which could lead to better awareness of the danger of malaria.
Bedtime after midnight was associated with "incorrect" compliance with the use of IIBNs and long clothing. In other studies, eveningness, a concept closely related to bedtime after midnight, has been associated with "incorrect" compliance with chemoprophylaxis . Eveningness is a multi-factorial variable with genetic and environmental components  and has been associated with certain personality traits and dimensions, such as extraversion, novelty seeking, impulsivity and anti-conformism . These results favour the hypothesis that there are common determinants of incorrect compliance, of which late bedtime could be a marker.
The perception of personal malaria risk and severity comprises the concept of threat perception, one of the two aspects of health behaviours in the "Health Belief Model" . In a previous study, the "Health Belief Model" combined with measures of perceived behavioural control was able to explain nearly half of the variance in reported adherence among mefloquine users and 40% of the variance among chloroquine and proguanil users . Moreover, travellers who perceived themselves to be at higher malaria risk were likely to be more compliant with malaria chemoprophylaxis [3, 11–13]. In the present study, the perception of lower personal malaria risk compared with other individuals was associated with "incorrect" compliance with the use of insect repellent but not with the other AVPMs, and the perception of the severity of malaria was not associated with compliance with any of the three AVPMs. Therefore, the perception of personal malaria risk and severity (i.e., the two aspects of individual representation of health behaviours in the "Health Belief Model") did not appear to have the same relationship with compliance with chemoprophylaxis. In accordance with the "Health Belief Model", these results suggest that even if the perceived probability of a threat and its perceived severity are the first two dimensions generating perception of risk and motivation for action, they are insufficient to predict any health behaviour. Perceived barriers appear to be the most powerful predictor of health action .
Medical history of malaria was associated with "correct" compliance with wearing long clothing and with "incorrect" compliance with the other AVPMs and chemoprophylaxis . These findings are comparable with the behaviours of patients with chronic diseases [28, 29]. Past experience of disease burden is insufficient to adopt appropriate behaviours against relapses. The weak associations between compliance with AVPMs and both a medical history of malaria and the perception of personal malaria risk and severity suggest that interventions based on cognitive approaches in reference to "bad experiences" could have little impact on compliance improvement.
Participating in field operations was associated with "correct" compliance with the three AVPMs. The same finding applied for chemoprophylaxis , suggesting that the two have the same determinants. In field operation-type stays, individuals may better perceive the risks and need for protection and may be under higher pressure from the staff to comply with security rules to prevent casualties in the context of a dangerous environment.
The prevalence of "correct" compliance with wearing long clothing and using IIBNs was higher in countries where the incidence rate of clinical malaria was known to be higher (i.e., from 7.5 and 9.0 clinical malaria cases/100 person-years in the Ivory Coast and Central African Republic, respectively) than in the other countries (from 0.1 to 2.1 clinical malaria cases/100 person-years in Djibouti and Gabon, respectively) during the 2005-2006 period, according to the French Forces epidemiological surveillance. Individually driven compliance and staff pressure to ensure "correct" compliance could be modulated according to the environment and the perceived or documented level of malaria risk. More favourable living conditions, such as sleeping in permanent structures or air-conditioned rooms during training or less intrusive missions, could have made individuals feel safer towards mosquito bites, thus impairing their compliance with AVPMs. Because a country was the theatre of only one type of stay (either for field operations or training), it was not statistically feasible to segregate the two variables.
The group effect remained significant in all three final multivariate models. Furthermore, the rate of compliance was heterogeneous between groups. These results suggest that individual behaviours were probably not independent within a group and that significant collective behaviour determinants were not identified in the present study.
Although this study was performed among French military personnel travelling for a four-month period in tropical Africa, the present results could be directly extrapolated to other aforementioned groups of non-immune workers staying in malaria-endemic areas. Extrapolation to individual travellers staying for a shorter duration is less straightforward due to the supposed absence of collective factors. However, data about compliance with AVPMs are scarce among such populations [5, 7, 11]. Thus, the present study could elucidate some of the determinants of the compliance of travellers with AVPMs. Moreover, a similar study to be conducted among civilian travellers would be difficult to perform, mainly because of sample size (more than 2,000 people in the present study), heterogeneity in data collection and exposure to malaria risk. Nevertheless, further studies should focus on cognitive and behavioural predictors of compliance of travellers with AVPMs.