Table 2.
Minimum Hypothetical and Expected Observed Prevalence Ratio to Detect an Outbreak of Microcephaly if Zika Virus Infection Risk Doubles, by Sensitivity and Specificity of Microcephaly Case Detection
| Microcephaly | TEM a(cm) | Sensitivity (%) | Specificity (%) | Prevalence ratio | |
|---|---|---|---|---|---|
| Hypothetical | Expected Observed | ||||
| All | 0.24 | 85.1 | 99.4 | 2.00 | 1.06 |
| 0.42 | 77.6 | 98.8 | 2.00 | 1.04 | |
| 0.71 | 91.2 | 97.2 | 2.00 | 1.03 | |
| Severe | 0.24 | 81.9 | 99.9 | 24.00 | 1.48 |
| 0.42 | 75.0 | 99.9 | 27.50 | 1.43 | |
| 0.71 | 65.9 | 99.6 | 39.50 | 1.33 | |
a TEM: Technical error of head circumference measurements. TEM = 0.71 came from Bhushan et al. (J Clin Epidemiol Vol. 44 (10):1027–1035, 1991), but values of sensitivity and specificity for all microcephaly were taken directly from their article, while those for severe were obtained by simulation. All other TEM values came from Onis (Acta Pædiatrica, 2006; Suppl 450:38–46) and were used to estimate sensitivity and specificity by simulation