High Dengue Case Capture Rate in Four Years of a Cohort Study in Nicaragua Compared to National Surveillance Data

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Abstract
Dengue is a major public health problem in tropical and subtropical regions; however, under-reporting of cases to national surveillance systems hinders accurate knowledge of disease burden and costs. Laboratory-confirmed dengue cases identified through the Nicaraguan Pediatric Dengue Cohort Study (PDCS) were compared to those reported from other health facilities in Managua to the National Epidemiologic Surveillance (NES) program of the Nicaraguan Ministry of Health. Compared to reporting among similar pediatric populations in Managua, the PDCS identified 14 to 28 (average 21.3) times more dengue cases each year per 100,000 persons than were reported to the NES. Applying these annual expansion factors to national-level data, we estimate that the incidence of confirmed pediatric dengue throughout Nicaragua ranged from 300 to 1000 cases per 100,000 persons. We have estimated a much higher incidence of dengue than reported by the Ministry of Health. A country-specific expansion factor for dengue that allows for a more accurate estimate of incidence may aid governments and other institutions calculating disease burden, costs, resource needs for prevention and treatment, and the economic benefits of drug and vaccine development. National public health and epidemiology programs are often tasked with tracking certain infectious diseases, but many barriers lead to under-reporting. In tropical and subtropical countries where dengue fever is endemic, under-reporting may be due to misdiagnosis, limitations of the WHO case classification, and lack of laboratory infrastructure or resources, among other issues. In Nicaragua's capital, Managua, we compared the number of dengue cases identified in a cohort study of 2- to 12-year-old children in one health center to the number of pediatric cases reported from all other municipal health centers in Managua to the National Epidemiologic Surveillance (NES) program. In the years 2004–2008, between 13 and 65 dengue cases were identified in the cohort (approximately 3,700 participants), and between 0 and 51 cases were reported by individual health centers in Managua. When the incidence per 100,000 people was calculated and compared, an average of 21 times more dengue cases were identified in the cohort study compared to the number reported to NES. Application of such an expansion factor may help governments and other health institutions to estimate the actual number of dengue cases in a population and therefore better allocate resources for prevention, treatment, and drug and vaccine development.