In addition, local mosquito abatement districts worked closely with the CDC to “conduct larval and adult mosquito surveillance in the 3 areas where the index patient (2 residences) and patient A resided.” This surveillance consisted of conducting household surveys and deploying traps (light, CO2, gravid, BioGent) to collect mosquitoes at sites by the residences.
The authors reported that all of the larvae and pupae collected at the 3 residences and nearby sites found only Culex
mosquito species. They also “failed to detect viable mosquito eggs,” and when reviewing the mosquitoes collected from the traps, the researchers “failed to detect the invasive species.”
According to the report, 226 households were within 200 miles of the 3 residences. Of those households, 89 had 1 resident or more completed the survey the CDC deployed; the rest were either unavailable, refused to take the survey, or “were unable to be interviewed in their native language.” Of the households that participated, 218 individuals answered questionnaires; of the 218 individuals, 124 gave a blood sample, 6 gave blood and urine samples, and 2 provided only urine samples. Of all the samples, 2 blood samples tested positive for Zika. However, they “were not confirmed by plaque reduction neutralization test (these samples were negative for Zika virus and dengue virus neutralizing antibodies).”
According to the report, the index patient was a unique case, not only because he died from the infection, but because he had a viral load that was about 100,000 times higher than average levels. Taking this into account, as well as the findings yielded from their investigation, the researchers concluded it is “likely that the index patient was the source of infection for patient A,” although they were unable to sequence virus obtained from patient A, and thus, they could not provide a “definitive confirmation.” However, the authors feel that these findings suggest that patient A’s infection “represents a rare transmission event through unknown, but likely, person-to-person mechanisms.”
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