Surveillance for an emerging disease: dengue hemorrhagic fever in Puerto Rico, 1988-1997. Puerto Rico Association of Epidemiologists.

Surveillance for emerging diseases is critically dependent on four factors: reporting methods, case definition, laboratory diagnosis, and knowledge of the disease among health-care professionals. The dengue hemorrhagic fever (DHF) surveillance system in Puerto Rico collects patient data from three sources: dengue case investigation (DCI) forms sent with diagnostic samples, clinical reports from hospital infection control nurses (ICNs), and hospital records. Recruitment of ICN reporting produced a marked increase in notifications (67 to 294). Hospital records of possible DHF cases showed that tests for ascertaining diagnosis (e.g., blood in stool, serum albumin) were frequently not performed. DCI and ICN reports underestimated severity. After hospital record review, the ratio of total DHF cases to cases detected by surveillance was approximately 3:1, whether using clinical criteria or using clinical and dengue laboratory diagnosis. An important determinant for the low sensitivity (28.4%) and high specificity (96.5%) of the surveillance system was the World Health Organization (WHO) clinical definition for DHF. In spite of such limitations, DHF surveillance data in Puerto Rico provide abundant, reliable information for monitoring disease trends. These methods may be applied to other situations to define the characteristics and incidence trends of emerging infections.