Table 4. Summary of the evidence on sexual transmission of Zika virus as assessed using the sexual transmission framework.
| Element | Value | Sample size | References | GRADE |
|---|---|---|---|---|
| 1. Susceptibility | Summary: based on animal models, rectal and vaginal mucosae are susceptible to infection. The testes form a reservoir for virus. Male–female transmission is more common than female–male transmission. | — | [32, 34–36, 40, 43, 47, 49, 51, 58, 59, 63] | NA |
| 2. Incubation period following sexual transmission | Could not be calculated | — | NA | |
| 3. Serial interval | Median: 12 days (interquartile range: 10–14.5) | 15 couples | [6, 78, 79, 84, 85, 88, 90, 96, 102, 115, 124, 131, 137] | Very low1 |
| 4. Duration of infectiousness | ||||
| Male genital tract RT-PCR (cohorts) | Median: 34 days (95% CI: 28–41) | n = 55 | [20] | Low2 |
| Median: 35 days, mean: 54 days (95% CI: 53–55) | n = 184 | [74] | Low2 | |
| Male genital tract RT-PCR (case reports and case series) | Median: 39.6 days (95% CI: 29.9–49.0) | n = 119 | [76,80,84–86,88–95,97,98,100,102,103,107,109,112,113,115–117,124,126,128–137] | Very low2,3 |
| Male genital tract viral culture | Median: 9.5 days (95% CI: 1.2–20.3) | n = 22 | [80, 84, 86, 92, 99, 103, 107, 112, 115, 126, 130] | Very low1,2,3 |
| Female genital tract RT-PCR | Median: 13.9 days (95% CI: 7.2–19.6) | n = 15 | [95, 104, 108, 110, 111, 114, 133] | Very low1,2,3 |
| Saliva RT-PCR | Median: 6.8 days (95% CI: 4.3–9.6) | n = 76 | [75, 81, 83–85, 89, 90, 92–94, 98, 99, 104, 110, 112, 122, 125, 126, 131, 133, 134, 138] | Very low1,2,3 |
| 5. Reproduction number due to sexual transmission | <1 | — | [139, 140] | Very low4 |
| 6. Probability of transmission per sex act | Could not be calculated | — | NA | |
| 7. Transmission rate | (Assumed) | — | NA | |
| Proportion of cases due to sexual transmission | 3.0% (95% CI: 0.1%–45.7%); 23% (95% CI: 1%–47%) | — | [139, 140] | Very low4 |
Estimates of the outcomes and publications that provide evidence for these different elements of the sexual transmission framework are listed by outcome. Additionally, the certainty assessment using Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology is provided.
1Small sample size or small number of studies.
2Indirect measure of duration of infectiousness.
3Risk of selection bias or selective reporting.
4Serious indirectness and imprecision.
NA, not applicable; RT-PCR, reverse transcription PCR.