Comparative performance of the probable case definitions of dengue by WHO (2009) and the WHO-SEAR expert group (2011)

Abstract

Background

The primary objective of this study was to find the performance of the 2009 probable case definition of dengue and compare it with the definition given by the WHO-SEAR expert group in 2011.

Methods

A cross-sectional study was conducted in Thiruvananthapuram district of Kerala, which is hyperendemic for dengue. A consecutive series of 851 participants defined by the selection criteria were recruited from the primary, secondary, and tertiary health care settings. Sensitivity, specificity, predictive values, and likelihood ratios of the clinical case definitions were calculated using reverse transcriptase-polymerized chain reaction (RT-PCR) as gold standard in case of fever less than or equal to 5 days and serology (IgM positivity) for fever >5 days. Diagnostic odds ratio (DOR) was also calculated as a single indicator of performance of the case definition.

Results

The 2009 World Health Organization (WHO) case definition had a sensitivity of 76·4% (69·6–82·1) and negative predictive value of 87·5%. The 2011 WHO-SEAR expert group case definition had a higher sensitivity of 87·9% (82·2–91·9) but lower negative predictive value of 86·6%. The three independent criteria which were significantly associated with dengue were thrombocytopenia less than 150 000 (OR 2·80), leukopenia (OR 2·28), and absence of backache (OR 2·68). The performance of 2009 case definition was better (DOR 2·4) than the 2011 WHO-SEAR expert group case definition. This was further enhanced when thrombocytopenia was specified as platelet count less than 150 000 (DOR2·7). When ‘no backahe’ was added as an additional criteria, the performance of both definitions improved.

Conclusions

The 2009 WHO case definition has better discriminatory power than the 2011 WHO-SEAR expert group case definition. The performance of 2009 WHO case definition is enhanced by specifying thrombocytopenia as platelet count less than 150 000. The inclusion of ‘no backache’ further improves the discriminatory power. This may be more useful in primary care settings, to rule out dengue.

Keywords:

• Dengue
• Case definition
• WHO
• SEAR
• Diagnostic odds ratio

Acknowledgements

We place on record our gratitude to the faculty of State Board of Medical Research (SBMR), especially our Principal Dr Ramdas Pisharody, for funding the study and giving the necessary support and guidance (Order No: A2-8557/2010/MCT). We gratefully acknowledge ICMR Virology Network Program, Government of India, as they funded the investigations done at Rajeev Gandhi Centre for Biotechnology, Thiruvananthapuram, Kerala, India. We thank the staff of the various institutions under the Directorate of Health Services for the support provided in the conduct of the study. We would like to mention a special word of gratitude to Dr Syam Sunder, general hospital, Thiruvananthapuram in this regard.

The interns posted in our department during the period had participated sincerely in the project and we wish to acknowledge their work as well.