Malaria is estimated to be directly responsible for around one million deaths annually worldwide ^[1]. The morbidity and mortality burden caused by malaria are responsible for nearly 3% of the world's DALYs ^[2]. Even though Africa accounts for 90% of the mortality burden for malaria, South-east Asia still suffers considerable mortality and morbidity. Malaria is a major public health problem in Bangladesh. Of the 11 countries of the World Health Organization South East Asian Regional Office, ten countries including Bangladesh are malaria endemic.

Due to the frequent use of DDT by the Malaria Eradication program of the then Government of East Pakistan, malaria was mostly under control before 1971 ^[3]. After the independence of Bangladesh from Pakistan, DDT was banned in 1985 and the number of malaria cases began to increase. Since the incidence of malaria in the eastern regions was low and there was a lack of adequate funds and programs, no control efforts maintained in the malaria endemic areas of Bangladesh. Without these control efforts, malaria cases started to increase and became epidemic in the 1990s ^[3], ^[4]. In the late 1990s, more than 500 deaths were reported with 70,000 laboratory-confirmed cases and 900,000 clinical cases of malaria in Bangladesh ^[5].

The number of malaria cases in Bangladesh fluctuates seasonally. The majority of these cases occur in the thirteen districts close to and/or bordering India and Myanmar. These thirteen districts, out of the 64 administrative districts of Bangladesh, are recognized as malaria endemic. Ninety eight percent of the malaria case reports come from these thirteen districts. Three out of these thirteen districts, Bandarban, Khagrachari and Rangamati, collectively known as the Chittagong Hill Tracts (CHT) districts, report the highest incidence of malaria within the country. These thirteen districts are difficult to reach due to the hilly terrain and therefore have inadequate passive surveillance and information systems resulting in poor reporting of malaria cases by the Ministry of Health, Government of Bangladesh ^[6], ^[7].

In 2006, the Global Fund for AIDS, TB and Malaria (GFATM), awarded Bangladesh USD 39.6 million to support the national malaria control program. These funds were used by the national malaria control program to start advocacy at community level, ITN distribution, introduction of rapid diagnosis test (RDT) and to introduce combined therapy with coartem. In the absence of baseline information, these resources could not be equitably distributed among the population. Furthermore, these data would be needed for future comparisons to assess the effectiveness of these programs. Therefore in 2007, BRAC and ICDDR,B carried out this first ever malaria prevalence survey of Bangladesh, the results of which are presented here.

In thirteen malaria endemic districts, the overall weighted malaria prevalence rate was 3.97% (Table 1). The survey clusters (see supplemental information file) and malaria prevalence maps were prepared (figure 2, 3 and 4 respectively). Figure two shows the survey cluster locations. The distribution of P. falciparum is presented in figure three. Plasmodium falciparum was found in eleven districts of the thirteen surveyed districts. The prevalence rate varied from 0.13% to 15.07%. Figure four, shows that P. vivax was found in ten districts; in which the prevalence rate varied from 0.13 to 1.2%. The weighted prevalence of P. falciparum was 3.58% and the P. vivax 0.21% and mixed infection with P. falciparum and P. vivax was 0.18%. The proportion of P. falciparum was 90.18% while P. vivax and mixed infection with these two species were 5.29 and 4.53% respectively in these thirteen districts. Prevalence of P. falciparum in males and females was 3.96% and 3.98% respectively. The prevalence of malaria was significantly higher in children. The prevalence of falciparum malaria in children 0?4 years of age was 8.5% and 5?14 years of age 6.6%. P. vivax prevalence among male are 0.15%, and female are 0.27%. Mixed infection prevalence among male and female were 0.21% and 0.15% respectively. In five south-eastern districts the average weighted prevalence rate was 6.00% while in the eight north -eastern districts average weighted prevalence rate was 0.40%. The overall malaria prevalence in Chittagong Hill Tracts (CHT) districts was 11.7%. The prevalence rate was 15.25%, 10.97% and 7.42% in Khagrachari, Bandarban and Rangamati districts respectively.

When we conducted the survey, we randomly identified one person and performed a RDT. We recorded whether this individual reported fever within last fifteen days. If he/she had suffered with fever within last fifteen days and was RDT positive, we considered that is morbid event. Malaria morbidity was found to be higher in the five south-eastern districts when compared to the eight north-eastern districts.

A total of 9750 participants in the study area, 300 were RDT positive and 9450 were negative. Please see the supplemental information (Table S1). Households of RDT positive participants were considered as malaria infected households and RDT negative participant's households are malaria non-infected households. Bednet use information of 9749 participants was used for statistical analysis and only one participant's information was missing. About 91.1% (n?=?267) and 93.7% (8799) participant's households had a bed net among the malaria positive and negative households respectively (p?=?0.118, not significant). We have also observed that the bed net use pattern in the infected and non-infected households and found that malaria infected households having significantly less number of bednets (<?=?2) compared to malaria non-infected households (Table 2). It was also found that significantly more malaria infected households are in the five south-eastern districts compared malaria non-infected households (Table 2). In the five south-eastern districts the percentage of bed nets treated with medicine within last six months were similar for both types of households. Table 3 shows the adjusted odds ratios (OR) for the variables using the logistic regression model. Independent risk factors for malaria infection found significant in multivariate analysis for the entire surveyed area when less than or equal to two bednets in household (OR?=?1.87, 95% CI?=?1.30?2.71) and households in south-eastern districts (OR?=?17.31, 95% CI?=?9.60?31.30).

In order to implement an effective malaria control program in Bangladesh, accurate information on the incidence and prevalence of malaria is required. In this study, the first malaria prevalence survey was conducted to provide the baseline parasitological information for population living in the malaria endemic districts of Bangladesh. This cross-sectional survey provides point prevalence data on malaria in these thirteen malaria endemic districts. These data will also be a massive help of global initiatives of malaria mapping ^[15].

We have found a much higher prevalence of malaria than would be expected by investigating the national passive surveillance information ^[16]. This indicates that by the passive surveillance conducted by the national malaria control program significantly underestimates the burden of malaria in these 13 malaria endemic districts, especially in the five south-eastern districts.

Given that no significant difference was found between male and female malaria prevalence rates, it can be concluded that the gender difference will not be an issue for malaria control. However, there were significantly higher rates of infection among children, thus indentifying a need for targeted interventions for young populations.

Malaria is not equally distributed in all malaria endemic districts of Bangladesh. Prevalence of malaria in five south-eastern districts is significantly higher than the eight north-eastern districts. Chittagong Hill Tracts (CHT) districts have the highest prevalence than the other endemic districts. The reason might be that CHT districts are hilly and covered with forest and lakes, provide an excellent habitat for malaria vectors ^[17]. Resources should be differentially targeted to this area given its larger malaria burden. The combined use of GIS (geographic information system) and remote sensing provides a significant tool to control malaria ^[18]. We hope GIS and high resolution satellite images can be used to detect malaria hot spots and vectors habitat sites, particularly in CHT districts, as part of our ongoing work.

From this study it is also clear that P. falciparum is the dominant species in the malaria endemic districts of Bangladesh, with the highest prevalence occurring in the CHT districts. This is of high concern since P. falciparum is known to be the most deadly and drug resistance for treatment of P. falciparum is a worldwide problem ^[19]. Risk factors regarding the use of bed nets in this study have been found to be consistent with similar studies conducted in Somalia ^[20]. This study also confirms the results obtained in Vietnam that the households having two or more than two bednets are more protective ^[21]. The use of two or more than two bednets in a household is an effective malaria control intervention in Bangladesh. Efforts should be focused to increase the supply of at least two bednets in the malaria endemic areas of Bangladesh, especially in the south-eastern districts of Bangladesh.

Total population in endemic areas are 26.9 million, and the risk exposure is as high as in many African countries ^[22], ^[23]. Longitudinal studies are needed to assess the variation of asymptomatic parasite carriage over time, and its exact contribution to transmission. Population-based prevalence studies on a regular basis are required to understand the burden of disease. More studies should be conducted in the future to map the changing malaria epidemiology in Bangladesh as control activities are scaled up.

Competing Interests: The authors have declared that no competing interests exist.

Funding: This study was implemented with Global Fund for AIDS TB and Malaria (GFATM) support. The project was jointly implemented by BRAC (BRAC is a brand name and it can't be expanded) and ICDDR,B (International center for diarrhoeal disease research Bangladesh). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

We are grateful for all field staff for collecting data.