In this series of cross-sectional studies in southern Zambia, knowledge of the symptoms, causes and prevention of malaria was high in the two study areas over three calendar years. The prevalence of malaria varied over the study period, from 23.9% in the 2007 study area to 8.1% and 1.5% in the 2008 and 2009 study area. Most infected individuals reported symptoms of malaria, although few had documented fever at the time of the study visit. In the first study area, when the prevalence of malaria was highest, several established characteristics were correlated with RDT positivity, including young age, reported symptoms, documented fever, failure to sleep under a bed net, rainy season and use of open water sources. In the second and third study years, with markedly lower malaria prevalence, few individual-level characteristics were correlated with RDT positivity.
Ascertaining and improving general knowledge of malaria is crucial to the acceptance and uptake of prevention practices in a community. The majority of participants in all years correctly identified the symptoms of malaria and knew that malaria was transmitted by mosquitoes. Similar to other regions , most participants acquired knowledge of malaria from health workers or at school. However, a considerable proportion of participants either did not report the correct cause of malaria or, as in other studies in the region [19–21], identified other causes primarily related to drinking and eating food. This lack of accurate knowledge regarding causes of malaria was reflected in the level of knowledge regarding preventive measures, particularly in 2007 when ITN distribution began in the area. As few as 40% of participants reported bed nets as a prevention measure, few other measures were identified, and many participants reported they did not know how to prevent malaria. The survey instrument was based on an allopathic concept of malaria and further ethnographic research is needed to explore the local taxonomy of illness and explanatory models prevalent in the community.
Bed net ownership varied from 40.9% to 77.0%; however, in all study years, approximately half of participants who owned an ITN did not sleep under it. The primary reason provided for not sleeping under a bed net was the absence of mosquitoes, suggesting seasonal use of ITN. Indeed, participants were more likely to report sleeping under an ITN during the rainy season, as reported in other studies . Other reported reasons for not sleeping under the bed nets were primarily logistical [19, 22]. These included an inability to hang the bed net or sleeping outside, which was particularly problematic for participants in 2008, changing sleeping places, difficulties sleeping under a bed net due to heat, crowding, or discomfort, and the bed nets being old or dirty. These factors and their impact on ITN use and subsequent protection from malaria infection need to be considered in control programmes to maximize the benefits of ITN.
The prevalence of malaria ranged from 23.9% in 2007 to 1.5% in 2009 in this study conducted over three calendar years and two geographical areas. In 2007, when transmission was highest, several well established risk factors correlated with infection, including younger age , presence of anaemia , using open water sources , sleeping without a bed net [3–5, 8], rainy season [5, 7], and self-reported or documented symptoms . However, in 2008 and 2009, when the prevalence of malaria was substantially lower, only self-reported or documented fever correlated with infection. With declining prevalence, malaria was no longer likely to be diagnosed in the rainy season or among individuals sleeping without a bed net. The median age of infected individuals increased from 9.0 years with high parasite prevalence to 12.5 and 13.2 years with low prevalence, and was no longer significantly different from the age of the general study population. This shift to higher age groups with declining transmission has been observed in other studies and settings [8, 23, 25]. Although the power to detect differences decreased with declining malaria prevalence, many characteristics correlated with RDT positivity in 2007 were not associated with RDT positivity in 2008 and 2009.
Only symptoms, particularly fever, correlated with RDT positivity in the time periods with low levels of parasite prevalence. When all symptoms of malaria were considered together, infected individuals were more likely to report symptoms and in greater numbers in 2007 and again in 2009. However, in all years, symptoms of malaria were highly prevalent in RDT-negative individuals, with up to 63% of RDT-negative individuals reporting symptoms within the 48 hours prior to the study visit, thus decreasing the specificity of symptoms in identifying infected persons. RDT-positive individuals were more likely to have documented fever in 2007 and 2008 but only 10-20% of positive individuals had fever. Most RDT-positive individuals were without fever at the time of testing. Other studies in various transmission settings found a large proportion (up to 96%) of individuals infected with malaria to be asymptomatic [26–28]. This finding poses a significant challenge to malaria elimination as many control strategies rely on the identification and treatment of symptomatic individuals seeking care at health centres .
This study was subject to several limitations. First, the study was conducted over two geographic areas. Participants surveyed in 2008 and 2009 were from the same geographic area, while those surveyed in 2007 were from an area further east. Consequently, it is possible that the different risk factors found between the two areas, was not due to the decline in malaria transmission but to differences in the ecology or characteristics and behaviours of the participants surveyed. When participants and households were compared, however, there did not appear to be many differences based on measured characteristics. Second, we did not collect information on behaviors, occupation, assets, migration, and travel that might be associated with malaria. Finally, as previously discussed, the power to detect associations was low in 2008 and 2009 with declining malaria transmission.