Assessing Sensitivity and Specificity of Surveillance Case Definitions for Zika Virus Disease

Angela Chow; Hanley Ho; Mar-Kyaw Win; Yee-Sin Leo


Emerging Infectious Diseases. 2017;23(4):677-679. 

In This Article

The Study

We evaluated the performance of surveillance case definitions for Zika virus disease recommended by the CSTE, WHO, PAHO, ECDC, and the Singapore MOH by using a cohort of 359 adult patients with suspected Zika virus disease who came to the Institute of Infectious Diseases and Epidemiology, Tan Tock Seng Hospital, Singapore, the national referral center for Zika virus disease during the containment phase of the Zika virus outbreak during August 26– September 5, 2016. All adults living or working in the outbreak area who were sick and had symptoms that partially or fully met the MOH definition were screened for Zika virus disease.

At their first visit to the hospital, all patients had their signs and symptoms documented, and blood and urine samples were obtained for detection of Zika virus nucleic acids by reverse transcription PCR (RT-PCR).[15] Parallel testing in the hospital laboratory and at the National Public Health Laboratory (Singapore) was conducted to maximize sensitivity and negative predictive values to rule out Zika virus infection.

A total of 42.0% of the cohort had Zika virus infection confirmed in blood (4%), urine (36%), or both (60%) samples (Table 1). Most (80%) infected and noninfected patients were tested ≤5 days after illness onset (infected patients, mean 3.6 days; noninfected patients, mean 4.6 days). Infected and noninfected patients were similar in age and sex. No female patients were pregnant. Among Zika virus–infected patients, rash (93.3%) was the most common symptom, followed by fever (79.2%) and myalgia (42.3%). Headache, arthralgia, and conjunctivitis were reported in <25% patients with Zika virus disease. Pruritus (11.4%) and gastrointestinal symptoms (6.7%) were relatively uncommon. For patients not infected with Zika virus, fever (86.2%) was the most common symptom, followed by myalgia (59.1%) and rash (44.8%).

The case definition recommended by CSTE for use in the United States (US definition) had a sensitivity of 100% and a specificity of 2% in detecting Zika virus in the cohort (Table 2). The WHO case definition had the lowest sensitivity (38%). The Singapore MOH case definition had a sensitivity of 54% and a high specificity of 76%, and performed well in diagnosing Zika virus disease (positive likelihood ratio [LR+] 2.2, 95% CI 1.7–3.0). The performances of PAHO (LR+ 2.1, 95% CI 1.5–2.8) and ECDC (LR+ 2.1, 95 % CI 1.6–2.8) case definitions were similar.