Puerto Rico case distribution consistent with observations in other Zika-infected settings, but not with other impacts of other mosquito-borne viruses, suggesting sexual transmission raises women’s risks
Results from nearly a year of testing Puerto Rico residents with suspected Zika illness reported by the U.S. Centers for Disease Prevention and Control today show more than 800 of every 100,000 island residents infected with the virus that causes a range of severe neurological birth defects, with infection rates highest among women, and incidence among them highest in those from 20-39 years old.
The data, from the Puerto Rico Department of Health, was collected from test outcomes between November 2015 and October 2016, and comprises information on the greatest number of confirmed cases worldwide. Of 62,500 people tested in Puerto Rico during that time, tests either confirmed or supported a finding of Zika infection among 29,345 patients. Pregnant women accounted for 1,126 of those infected. Because pregnant women were viewed as likelier to seek health care, and be tested for Zika than other populations, researchers separated data on nonpregnant patients. Of those, 61 percent were female. In addition, among patients 40 years or older who were tested, women were likelier be confirmed to have the virus, than men.
The findings, reported in the CDC’s Morbidity and Mortality Weekly Report are consistent with patterns observed in Brazil and El Salvador, where the greatest numbers of people reported to have the virus fell between 20 and 49, the authors write. But, the authors also note, the pattern of the Zika data differs from patterns dengue and chikungunya infection in Puerto Rico during outbreaks of those illnesses spread by the same species of mosquito.
The authors conclude higher rates of infection among women, and among those of child-bearing age could be the result of greater susceptibility to infection, greater exposure to the mosquito that carries the virus, differences in how the virus affects women, differences in health care seeking, and health care worker responses, and, reflect greater risks of exposure from male-to-female sexual transmission.