Table 4.
Expected Observed Prevalence Ratio of Severe Microcephaly and Proportion of False Positive Cases During an Outbreak of Zika Virus Infection, by Increase in the Prevalence of Microcephaly in Newborn of Infected Mothers, and Sensitivity and Specificity of Microcephaly Case Detection
| HRIZ → M in prevalence ratioa | Intra-observer TEMb | Prevalence ratio c | Sensitivity (%) | Specificity (%) | Expected observed prevalence ratio | Proportion of false positives (%) |
|---|---|---|---|---|---|---|
| 1 | 0.24 | 1.00 | 81.9 | 99.9 | 1.00 | 34.7 |
| 5 | 0.24 | 1.21 | 81.9 | 99.9 | 1.14 | 24.7 |
| 10 | 0.24 | 1.35 | 81.9 | 99.9 | 1.26 | 18.4 |
| 15 | 0.24 | 1.50 | 81.9 | 99.9 | 1.41 | 14.7 |
| 1 | 0.71 | 1.00 | 65.9 | 99.6 | 1.00 | 82.5 |
| 5 | 0.71 | 1.21 | 65.9 | 99.6 | 1.06 | 74.5 |
| 10 | 0.71 | 1.35 | 65.9 | 99.6 | 1.10 | 66.8 |
| 15 | 0.71 | 1.50 | 65.9 | 99.6 | 1.16 | 60.5 |
a HRIZ → M: Hypothetical relative increase in the prevalence of microcephaly
b TEM: Intraobserver technical error of measurement of head circumference
c Prevalence ratio of microcephaly (outbreak vs non-outbreak period) under perfect diagnostic sensitivity and specificity