Since 2016, the World Health Organization (WHO) and other agencies have recommended a 6-month period of abstinence or barrier use to reduce the risk of sexually transmitted Zika infection upon return from an endemic country. Now, a study today in PLoS Medicine suggests that period may be unnecessarily long.
"This is a nice example showing how the accumulation of evidence can reduce uncertainty," Nicola Low, PhD, from the University of Bern, told CIDRAP News.
Low and her colleagues conducted the systematic review of evidence published through Apr 15 concerning the sexual transmission of Zika and other arthropod-borne flaviviruses in humans and other animals.
The studies were viewed through seven criteria: rectal and vaginal susceptibility to infection, incubation period following sexual transmission, serial interval between the onset of symptoms in a primary and secondary infected individuals, duration of infectiousness, reproduction number, probability of transmission per sex act, and transmission rate.
The investigators analyzed 128 studies, of which 77 were based on humans and 51 on animals. Sexual transmission between people was documented in 36 couples (34 male-to-female). The median serial symptom onset interval in 15 couples was 12 days (interquartile range, 10 to 14.5); the maximum was 44 days.
Zika RNA was present in semen for a median duration of 40 days (95% confidence interval [CI], 30-49 days) and a maximum duration of 370 days; in vaginal fluid, Zika RNA was found for a median duration of 14 days (95% CI, 7-20 days), with a maximum duration of 37 days (very low certainty). Infectious virus in human semen was detected for a median of 12 days (95% CI, 1-21 days) and a maximum of 69 days.
Research will be presented to the WHO
Though establishing absolute risk parameters is difficult, Low said she and her team are reporting their findings to the WHO, and as part of an expert panel, will likely recommend reducing the 6-month period for safer sex or abstinence.
"The recommendations will update the interim guidelines for the prevention of sexual transmission of Zika virus, which were published when the evidence was very sparse," Low said.
Low explained that the 6-month timeframe recommended was based on "random highs" — extreme values in a distribution that are observed by chance, and are more likely to be reported because they are noteworthy.
For now, Low said her team will maintain the living systematic review and develop a study protocol that can be used to monitor the sexual transmission of Zika in endemic countries.
See also:
Jul 24 PLoS Med study
