Trends in the knowledge, attitudes and practices of travel risk groups towards prevention of malaria: results from the Dutch Schiphol Airport Survey 2002 to 2009

The survey was conducted as previously described [3, 4]. In brief, self-administered, anonymous questionnaires were randomly distributed at the departure gate of Schiphol Airport, Amsterdam, The Netherlands, while passengers were waiting to board. Intercontinental flights to destinations with an intermediate or high risk for hepatitis A, hepatitis B or malaria were preferably selected. The survey was always done in the same period of the year, namely the months October or November. Travellers participated on a voluntary basis; no incentive was provided, except for a leaflet with information on hepatitis A, hepatitis B and malaria. Trained interviewers were present to distribute the questionnaires, to answer questions if necessary and to check the completeness of the responses collected. When possible, these interviewers copied the information from the travellers’ vaccination records. Travellers were allowed to participate if they were 18 years of age or older, and able to fully understand the language of the questionnaires. They also had to be resident in the Netherlands; thus, nationals of a developing country were only asked to participate if they were actually living in the Netherlands. These criteria were checked by the interviewers when distributing the forms. Afterwards, completed questionnaires from travellers who did not meet all the inclusion criteria were either excluded by the interviewers or rejected from the final analysis.

Two kinds of questionnaires were distributed among the participants, depending on the precise destination. The malaria questionnaire (Q-mal) focused on malaria and its prevention and treatment and these questionnaires were distributed only to travellers with destinations in or close to malaria-endemic areas. The vaccine questionnaire (Q-vacc) targeted the vaccine-preventable travel-related diseases hepatitis A and B. Both questionnaires had a common part on personal characteristics (age, gender, nationality, residence, profession), on information regarding the travel (destination, duration, purpose, travel companions) and its preparation, and on the travellers’ perception of the risk of malaria, hepatitis A and hepatitis B at their destination. However, since most malaria-endemic countries also carry a high risk for hepatitis A and B, the Q-mal questionnaire also contained several items dealing with the KAP towards prevention of hepatitis A and B.

Respondents with an age over 60 years were arbitrarily classified as elderly travellers. Solo travellers were defined as those travellers who travelled alone. Business travellers were defined as those travellers who specifically stated that their main purpose for travel was business-related. Last-minute travellers were defined as those travellers who did not seek pre-travel health advice or sought it only within two weeks before departure. Respondents who specifically stated that their main purpose for travel was to visit friends and relatives were considered VFRs.

Knowledge of malaria was determined by comparison of the risk for malaria as perceived by the traveller with the actual risk for malaria, as described [5]. To that end, all destinations (including those in malaria-endemic countries) were rated as low or high-risk destination for malaria based on maps published by the Centers for Disease Control, Atlanta, USA [6]. Destinations rated as low-risk also comprised destinations without any risk of malaria (no-risk area). For each subject the accuracy (correct risk perception) was expressed as 0 or 1, with 1 assigned to a subject if his (her) knowledge about risk was compatible with the official risk rating of the destination. To determine the attitude (intended risk taking or risk avoiding behaviour) of participants towards prevention of malaria, all participants were asked if they were planning to: (1.) cover their arms and legs when going outside; (2.) use of an insect repellant on uncovered skin; (3.) keep the doors and windows closed; (4.) sleep under a bed net and (5.) stay in air-conditioned surroundings. Each affirmative answer was scored with 1 point whereas a negation was scored with 0 points. The final attitude score towards prevention of malaria was obtained as the sum of the separate answer scores and could therefore range from 0 to 5; for convenience, the score was transformed to a 0–100 scale with the maximal protective attitude score set at 100. To have an indication of their practice (protection rate) towards prevention of malaria travellers were asked whether they had packed personal protective measures like insect repellents, bed nets and malaria chemoprophylaxis for this trip. Protection rate was expressed as a weighted sum of use of insect repellent (1 point), use of bed net (2 points) and use of malaria chemoprophylaxis (3 points). The practice sum score could, therefore, range from 0 to 6; for convenience, the score was transformed to a 0–100 scale with the maximal practice score set at 100. In order to estimate the impact of KAP of the travel risk group of interest on relative risk for malaria, a composite risk estimate was constructed by summing up the effects of the separate determinants. To that end, it was assumed that either a poor risk perception, intended risk-seeking behaviour or poor protection rates led to an equal increase in relative risk for malaria.

Several statistical analyses were made between travellers to high- and low-risk destinations: on one hand the so-called “between malaria risk destinations” analysis: e.g. the comparison of VFRs travelling to a destination with a high malaria risk vs VFRs travelling to a destination with a low malaria risk and on the other hand the so-called “within malaria risk destination” analyses: e.g. the comparison of solo-travellers to destinations with a high malaria risk vs the remaining (non-solo) travellers to this high malaria risk destination. To that end firstly differences in the predefined risk factor distributions between the two different risk destinations were tested using multiple logistic regression analyses, adjusted for subpopulation (maximally 14 subpopulations: two kinds of questionnaires by 7 interview years). Next, similar logistic regression analyses with adjustment for subpopulation were done for testing differences in risk (e.g., yes vs no VFR as independent variable) between the two knowledge groups (accurate risk perception y/n as dependent variable), allowing separate tests within low and within high risk destinations through entering the appropriate interaction terms into the models. The dependency of the attitude and practice scores on the risk factors was analyzed using multiple linear regression analyses, modeled similarly to the above mentioned logistic regression analyses. Those regression analyses also allow testing differences between the two risk destination groups in knowledge, attitude and practice within specific risk groups. Finally, it was tested by entering the appropriate interaction terms in the multiple logistic and linear regression models if the strength of the effect of the predetermined risk factors on knowledge, attitude and practice showed a significant time trend over the years 2002 to 2009 within low as well as within high risk destinations.

Across all seven years in the period from 2002 to 2009 (except year 2006), a total of 3,050 questionnaires were received, of which 3,045 fulfilled the entry criteria and were included in the analysis (Figure 1). Of the 3,045 respondents, 708 respondents travelled to destinations with a high risk for malaria. The remaining 2,337 respondents travelled to a low malaria risk destination. The general characteristics of all respondents, grouped by malaria risk in high and low risk destinations, are shown in Table 1. Overall, 46.4% of responders were female and 53.6% were male. Almost 71% of the travellers to high malaria risk destinations had malaria chemoprophylaxis (proguanil 3.0%; mefloquine 6.6%; doxycycline 1.0%; atovaquone/proguanil 47.0%; other 12.7%) with them and had packed insect repellents. Of the 1,324 travellers to a destination without malaria risk, 12 (0.9%) had packed malaria chemoprophylaxis.

For 20.8% of the travellers since 2004, it was their first trip to a developing country (there was no first-trip-item in the questionnaires of 2002 and 2003). Overall, 63.9% indicated tourism as their purpose of travel. One in five to six responders were visiting friends and relatives, business travellers accounted for 15.0% . Few responders travelled for missionary reasons or for voluntary missions (2.2%), for purpose of research or education (0.7%) or for other reasons (1.0%). Many travellers (41.6%) were accompanied by their partner or spouse; 869 persons (30.3%) were travelling alone, 6.9% with friends, 11.7% with children.

Travellers to high malaria risk destinations planned to stay significantly longer on their destination than travellers to low-risk destinations (p < 0.001) and obtained pre-travel health advice more frequently prior to departure (p < 0.001). Overall, 24.1% went abroad for 1 to 7 days, 40.2% for 8 to 14 days, 26.1% for 15 to 28 days, and 9.5% for more than 28 days. The Gambia was the most common high-risk destination (52.7%), followed by Surinam (14.3%) and Ghana (9.3%) whereas among the low risk destinations Turkey (18.3%) was the most common destination, followed by the Egypt (17.9%) and Mexico (7.7%) (Table 1).

The majority of travellers (65.5%) had sought health information about their destination prior to departure. This was done more than one month before leaving by 47.5% of the responders; 25.1% started preparing two weeks to one month before departure, 15.7% did so one to two weeks in advance, and 11.6% did so less than one week before leaving.

Of those who had not sought health information, the majority stated that they already knew what to do. The most common sources since 2004 for travel health advice to high risk destinations were the travel clinic or public health service (27.8%) followed by general practitioner (GP) or family doctor in 11.8% of the respondents. For low risk destinations the travel clinic or public health service was consulted more frequently in 51.0% of the respondents, whereas the GP or family doctor was consulted in 10.2% of the cases (p = 0.005). In the 2002- and 2003-questionnaires there was no item concerning source of advice. There was a significant positive trend over the years in the proportion of travellers to high-risk destinations seeking travel health advice (p = 0.002).

The group of elderly travellers comprised 439 respondents. Of them, 128 (29.2%) travelled to a high-risk destination. The group of last-minute travellers comprised of 545 respondents; 194 (35.6%) of them travelled to a high-risk destination. Of all respondents, 869 respondents travelled alone and were classified as solo-travellers; 209 (24.1%) of them travelled to a high-risk destination. The group of business travellers consisted of 453 individuals of whom 102 (22.5%) travelled to destinations rated as a high-risk destination. The group of VFRs consisted of 521 respondents; 390 (29.6%) of them travelled to a high-risk destination (Table 1).

Questionnaire-based surveys may have some drawbacks, which may limit the generalizability of the current findings. For instance, this study was designed to study the KAP of travellers to destinations with a high or lower risk for malaria and all destinations were selected to meet this requirement. The destinations were not randomly selected from all available risk destinations. Further, the survey was always done in the months October and November of each year, which may have introduced a selection bias since people who travel at this time of year may differ from people who travel during summer vacation. Moreover, one could argue that the traveller’s KAP profile including those belonging to risk groups may be influenced by their prior travel experience. To specifically address this potential confounder, all questionnaires since 2004 contained questions elaborating on this item but no significant differences in prior travel experience were found between travellers to high or low-to-intermediate risk destinations. Lastly, not all respondents belonged mutually exclusive to one risk group; this may limit the effect attributed to a certain characteristic of a risk profile.

In conclusion, the results of this questionnaire-based survey suggest that protection rates of Dutch travellers against malaria increase every year in concert with an annual reduction in intended risk-seeking behaviour. Last-minute travellers to high-risk destinations were identified as the risk group with the highest increase in relative risk for malaria underlining the continuous need for education, proper personal protective measures and malaria chemoprophylaxis of this travel risk group.