Comparisons of dengue illness classified based on the 1997 and 2009 World Health Organization dengue classification schemes

Background/Purpose: Dengue cases, traditionally classified as dengue fever (DF) or dengue hemorrhagic fever (DHF) by the World Health Organization (WHO) dengue classification 1997 scheme, are categorized into Group A (without warning signs), Group B [with warning signs (e.g., abdominal pain/vomiting/fluid accumulation/mucosal bleeding/lethargy/liver enlargement/increasing hematocrit with decreasing platelets)], or Group C (severe plasma leakage/severe bleeding/organ failure) by the WHO 2009 version. We compared differences in clinical/laboratory features between patients separately classified as DF/DHF and in Group A/B/C. Methods: We performed a retrospective analysis of dengue patients diagnosed between 2008 and 2010. Results: A total of 148 adult patients (119 DF/29 DHF; 64 Group A/77 Group B/7 Group C) were included. Compared with DF, significantly younger age, lower hospitalization rate, and higher platelet count were found in Group A. Compared with DHF, higher platelet count was found in Group B. Six of seven patients (86%) classified as Group C fulfilled the criteria of DHF. A cross tabulation showed DF cases were distributed in all of the severity groups stratified by the WHO dengue 2009 scheme (53.8% Group A/45.4% Group B/0.8% Group C); of the DHF cases, 23 (79%) were categorized as Group B, and six (20.7%) as Group C. All patients in Group A fell into the category DF. Conclusion: The WHO 2009 scheme is effective in identifying severe dengue cases. Heterogeneity in severity suggests careful severity discrimination in patients classified in Group B is needed. Our data suggest that it is safe to treat patients classified as Group A on an outpatient basis.