https://admin.imcjms.com/ Ibrahim Medical College Journal of Medical Science Saika FarookFarhan MuhibMaisha IslamMd. Faizul AhasanAunta MelanSadia IslamMd. Shariful Alam Jilani* https://admin.imcjms.com/registration/journal_full_text/619 2026-10-19 10:17:34 Brief Research Note July 2026; Vol. 20(2):005 40 years (58·1%), compared with <18 years (48·8%). Dengue represented a smaller proportion within each age group, peaking at 9% in those aged 18–40 years, while co-infection remained low (≤1·7%). Differences across age groups were not statistically significant.   Table: Distribution of RT-PCR–confirmed chikungunya (CHIKV) and dengue (DENV) infections (n=970)     Significantly greater proportion of males had CHIK compared with females (59·6% vs 54·9%; p=0·036), and co-infection was also significantly higher among males (2·5% vs 0·4%; p=0·008), whereas dengue proportions were similar between both sexes (p=0·089). Majority of CHIK cases presented in July (60·1%) and peaked in August (68·1%) before declining in September (45·7%; p<0·001). In contrast, DEN infection represented a small proportion in July and August (~3%) but increased significantly in September (13·4%; p<0·001). Co-infection peaked in August (2·7%; p=0·030). Overall, temporal variation and sex, but not age, were significantly associated with infection distribution. Among the 15 patients listed in the separate co-infection dataset, platelet counts were available for 13 patients (86.7%). Using a reference range of 150-450×10⁹/L for platelet count [7], 5 of the 13 patients (38.5%) had platelets counts below the lower reference limit. The remaining eight patients (61.5%)hadplateletcountswithinorabovethereferencerange. The lowest recorded count was 40×10⁹/L, indicating marked thrombocytopenia in at least one co-infected patient.   Discussion The occurrence of DEN-CHIK co-infection has been recognized for more than six decades. The earliest documented cases were reported in Thailand by Nimmannitya et al., who identified4 co-infected patients among 150 individualswith either DEN or CHIK during 1962–1964, corresponding to a co-infection rate of2.6% [8]. Since then, sporadic and outbreak-associated co-infections have been reported from several endemic countries. A large outbreak inPunjab, India, in 2009 reported a remarkably higher co-infection rate of54%, reflecting intense simultaneous transmission of both viruses [9]. Outside Asia, co-infections have also been documented in Africa and the Middle East. During an outbreak in Gabon, 8 of 773 patients (1.0%)were confirmed to have concurrent DEN and CHIK infections [10]. Similarly, in Al Hudaydah, Yemen,13 of 400 patients (3.3%) were diagnosed with DEN–CHIK co-infection during the 2012 outbreak [11]. These studies collectively demonstrate that although DEN–CHIK co-infection has been recognized for decades, its prevalence varies widely across geographical regions and outbreaks, ranging from less than 1% to more than 50%, depending on local transmission dynamics, vector abundance, timing of epidemics, and the laboratory methods used for diagnosis. In the present study, the prevalence of DEN–CHIK co-infection was1.5% (15/970), which is comparable to the relatively low rates reported from Thailand (2.6%), Gabon (1.0%), Yemen (3.3%), and Vellore (0.2%) [8,10-11] but substantially lower than the unusually high prevalence observed during the Punjab outbreak [9]. The low frequency of co-infection in our study may be explained by the differing epidemiology of the two viruses during the study period. Although both viruses were circulating concurrently in Bangladesh, CHIKV predominated during July and August, whereas DEN cases increased sharply in September, resulting in only a limited period of overlapping transmission. Furthermore, differences in viral transmission dynamics, mosquito infection rates, seasonal variation, vector competence, host immunity, healthcare-seeking behaviour, and study design may have influenced the likelihood of simultaneous infection. The use of multiplex real-time RT-PCR in the present study also ensured laboratory confirmation of acute infections, minimizing misclassification and providing a more accurate estimate of the true burden of co-infection compared with studies relying solely on serological assays. The higher proportion of CHIKV in July–August followed by a rise in DENV in September suggests aclassical seasonal pattern with sequential dominance, where ecological conditions during early monsoon may favor CHIKV transmission, and later conditions (e.g., increased vector density, viral amplification, or herd immunity shifts) facilitate DENV predominance. This indicates thatco-circulating arboviruses do not necessarily peak simultaneously but may alternate in dominance within the same season. This is biologically plausible in Bangladesh, where monsoon rainfall, temperature, vector density, and urban breeding conditions strongly influence the transmission of Aedes mosquito [3]. However, in case of DENV, a recent reporting of 24,535 cases in November and 8,165 in December months, typically considered low-risk months, suggests while peak transmission remains seasonally structured, DENV transmission is no longer strictly confined to the mid-monsoon period only (mid- June to mid-August). Instead, there appears to be a prolonged tail of transmission extending into traditionally low-risk months [3]. Althoughco-infection was infrequent, its detection is epidemiologically important. Since DENV and CHIKV share the same principal vectors, Aedes aegyptiandAedes albopictus, co-infection is expected wherever both viruses co-circulate [3]. Furuya-Kanamori et al. revealed that reported co-infection likely underestimates the true burden because many suspected arboviral cases are tested for only one pathogen [12]. The said article reported that 13 out of 98 countries or territories have been identified to report DEN and CHIK co-infection [12]. In this study,age was not significantly associated with infection distribution, indicating that exposure was relatively broad across age groups. By contrast, males had a significantly higher proportion of CHIK and DEN-CHIK co-infection, which may reflect differences inmobility, occupational exposure, and daytime contact with Aedes mosquitoes, which are predominantly day-biting [3]. Similar sex-related variation has been inconsistently reported elsewhere, suggesting that this may be influenced bylocal epidemiologic and behavioral factors rather than a universal pattern [1].   Cite this article as: Farook S, Muhib F, Islam M, Ahasan MF, Melan A, Islam S, et al. Dengue and Chikungunya virus co-infection in fever cases attending a tertiary care hospital in Dhaka city. IMC J Med Sci. 2026; 20(2):005. DOI:https://doi.org/10.55010/imcjms.20.014]]> 2026 Ibrahim Medical College. All rights reserved.