Dengue fever is emerging as a threat to public health in Bangladesh. It was prevalent among febrile patients who came to the six tertiary hospitals in our study and was equally prevalent in rural and urban residents irrespective of travel history. In comparison, only four malaria cases were detected at the study sites.
A previous hospital-based study of dengue infections in Bangladesh was conducted in September–October 1999 during the peak post-monsoon season in four of the same metropolitan cities.5
Eighteen percent of 200 patients had IgM antibodies against dengue virus identified by an ELISA dot technique. The data from our study, which were collected nationwide over a period of one year, confirms the importance of dengue as a cause of febrile illness in Bangladesh throughout the year ().
Dengue was previously assumed to be an urban disease because most cases have been reported from large cities.14–17
Our study found that dengue was equally prevalent among urban and rural residents. This finding supports results of other published studies on this trend.18–22
The spread of dengue in cities might be caused by unplanned urbanization, which produces environments that support increased vector reproduction, exposure to susceptible populations, and virus propagation.16,23–29
In the past several decades, dengue cases have been detected in rural areas in Thailand, Indonesia, India, Malaysia, Peru, Brazil and Cameroon.30–33
The vector for dengue transmission and dengue virus antigen in mosquitoes has also been detected in these regions.34–37
Technological advancement in villages leading to changes in rural ecology may also be a factor in dengue transmission among rural residents.38
Most dengue patients identified during this study were male (70%), but male patients were also more likely to be enrolled in the study (63%). This difference likely resulted from different health care utilization among male and female patients which is typical in South Asia.18
The proportion of female febrile patients who were positive for dengue (8%) was similar to that of male febrile patients (11%), and the difference was not statistically significant (P
> 0.2). Similarly in a study conducted during September 1996–June 1997 in Chittagong Medical College Hospital in southern Bangladesh, the proportion of female patients who were positive for dengue was 10% compared with 16% among males, a difference that was not statistically significant (P
During the 2000 dengue hemorrhagic fever outbreak in Bangladesh, a study conducted in Khulna Medical College Hospital in southern Bangladesh found no significant sex difference among the enrolled pediatric dengue patients: 62 boys (53.9%) compared with 53 girls (46.1%).40
Additionally, there was no significant sex difference either in a study in Thailand with male and female infants (male:female ratio = 1.3:1), or in studies in Brazil and Peru with older patients.41–43
Dengue fever has a reported case-fatality rate of approximately 1%, and the clinical consequences can be a serious issue for populations in Bangladesh.44,45
In this study, there was one death, and most (82%) patients recovered without any residual illness.
Malaria was not a major cause of febrile illness in this study population. We found few patients with malaria who came to the six tertiary study hospitals. This finding may have been caused by community malaria detection, treatment, and control initiatives implemented by BRAC and other non-government organizations through the Government of Bangladesh/GFATM.11,46
It could also be because we had study sites in only two of the designated malaria-endemic areas.8
We detected two malaria cases in a malaria-endemic area and an additional case who had traveled to a malaria-endemic area. Another explanation for the low case reporting could be that our study might have systematically enrolled patients who had failed anti-malarial therapy. Rural residents of Bangladesh generally visit pharmacies first, which commonly dispense anti-malarial drugs for treatment of illnesses.47,48
Patients who visit the hospitals would be expected to be biased towards those who failed to respond to the anti-malarial therapies in the community.
This study had several limitations. First, infections from malaria and dengue can have annual variations.49–52
Our study collected data for only one year, and so this could have been an unusually high or low year for either infection. However, the proportion of identified patients with dengue is consistent with the results from the study performed in metropolitan areas in 1999.5
A second limitation is the relatively small sample size used to assess the prevalence of rare diseases among febrile patients who came to the tertiary-level hospitals throughout the country. The small number of cases makes overall and especially regional-based estimates of prevalence imprecise. However, we do have data from six hospitals over the course of the year that provides strong evidence that malaria was not a leading cause of febrile illness among these patient populations during this time.
Third, we did not collect dengue convalescent-phase serum samples. We collected samples during 1–10 days of symptom onset. Among the 319 patients enrolled in the first four days of illness, some may have been infected with dengue, but had not yet developed antibodies against dengue infection.53,54
Therefore, our data may have underestimated the overall prevalence. However, this is likely a minor effect because the prevalence of IgM antibodies against dengue was similar among patients who came to a hospital within the first four days of symptom onset (9.4%) compared with patients who came to a hospital within 5–10 days of symptom onset (9.7%). Moreover, the sensitivity of the assay was high, ranging from 83.5% to 96.8%, as reported in several studies,55–58
irrespective of the sample collection period from the onset of illness.
Fourth, because antibodies to other pathogens including other flavivirus infections such as yellow fever and Japanese encephalitis and non-flavivirus infections such as leptospirosis can cross react with the dengue ELISA,59
it is possible that some of the dengue IgM antibody positive results are false-positives. Therefore, we may have overestimated the proportion of febrile illness caused by dengue virus. However, the high specificity (99%) of the PanBio (Windsor, Queensland, Australia) IgM ELISA reported in several studies suggests that few of our cases were misclassified.56,57,60
In Bangladesh, dengue is a year-round threat in urban and rural areas. As vaccine trials continue,61,62
a community-based dengue vaccination campaign could be piloted and evaluated as a possible prevention strategy. Physicians and health workers in rural areas should be trained to effectively manage dengue patients with adequate rehydration, follow-up and judicious use of antibiotics. The World Health Organization has recently recommended universal parasitological diagnosis for malaria irrespective of age groups and transmission settings.63
Thus, healthcare providers in Bangladesh should consistently use malaria diagnostics to ensure accurate diagnosis of febrile illness and to reduce inappropriate use of anti-malarial drugs. When laboratory diagnosis is unavailable, decisions about empiric use of anti-malarial drugs should take into account local malaria prevalence and any potential recent exposures to malaria during travel.