DENGUE SEVERITY THROUGHOUT SEASONAL-CHANGES IN INCIDENCE IN PUERTO-RICO, 1989-1992

To determine whether the proportion of severe dengue cases increased w ith the yearly seasonal increase in dengue incidence, we examined repo rts of disease symptoms in case surveillance data and laboratory testi ng results in Puerto Rico from January 1989 to July 1992. A computer a lgorithm was designed to identify severe cases, i.e., those that fulfi lled three or all four of the World Health Organization criteria for d engue hemorrhagic fever (DHF). A monthly severity index (SI) was defin ed as the ratio of severe cases to laboratory-positive and indetermina te (all non-negative) cases for each month, while a more restrictive s everity rate (SR) was defined as the ratio of severe laboratory-positi ve cases to the total number of laboratory-positive cases for each mon th. Monthly SI and SR were compared in two ways: within an epidemic cy cle, and month-by-month. Linear regression analysis was performed over the monthly averages of the SI and SR. For a month-by-month examinati on of SI and SR, we examined the 43-month sequence by means of a Linea r model with autocorrelated disturbances. We found no statistically si gnificant or cyclical change in the proportion of severe cases from mo nth to month in this period. Our conclusions differ from the observati ons during the Cuban DHF epidemic of 1981, in which case severity was shown to increase markedly as the epidemic progressed; they agree with the conclusions of most previous studies in that dengue severity does not change significantly throughout a period of increased incidence.