An Evaluation of modified case definitions for the detection of dengue hemorrhagic fever

RESUMO

The case definition for dengue hemorrhagic fever (DHF) requires fever, platelets < or = 100,000/mm3, any hemorrhagic manifestation, and plasma leakage evidenced by hemoconcentration > or = 20 percent, pleural or abdominal effusions, hypoproteinemia or hypoalbuminemia. We evaluated the specificity and yield of modified DHF case definitions and the recently proposed World Health Organization criteria for a provisional diagnosis of DHF, using a data base of laboratory-positive and laboratory-negative reports of hospitalizations for suspected dengue in Puerto Rico, 1994 to 1996. By design, all modifications had 100 percent sensitivity. More liberal criteria for plasma leakage were examined 1) adding as evidence a single hematocrit > or = 50 percent (specificity 97.4 percent); 2) accepting hemoconcentration > or = 10 percent (specificity 90.1 percent); and 3) accepting either hematocrit > or = 50 percent or hemoconcentration > or = 10 percent (specificity 88.8 percent). The new DHF cases identified by these definitions (and percent laboratory positive) were 25 (100.0 percent), 95 (90.5 percent), and 107 (91.6 percent), respectively. In contrast, the provisional diagnosis of DHF (fever and hemorrhage, and one or more of platelets < or = 100,000/mm3, or hemoconcentration > or = 20 percent, or at least a rising hematocrit [redefined quantitatively as a 5 percent or greater relative change]) showed a specificity of 66.8 percent, and identified 318 new DHF cases, of which 282 (88.7 percent) were laboratory-positive. Very small changes in the criteria may result in a large number of new cases. The modification that accepted either hematocrit > or = 50 percent or hemoconcentration > or = 10 percent had acceptable specificity, while doubling the detection of DHF-compatible, laboratory-positive severe cases, but ®provisional diagnosis® showed even lower specificity, and may produce inflated DHF incidence figures. Modified case definitions should be prospectively evaluated with patients in a health-care facility before they are recommended for widespread use.