Investigations of Two Cases of Isolated Local Transmission of Zika Virus
As of July 22, 2016, among the 321 cases of Zika virus infection in Florida residents or visitors, Miami-Dade County and neighboring Broward County reported the highest and second highest numbers of cases in Florida (93 and 51, respectively), accounting for 30.4% and 16.7% of travel-associated cases in nonpregnant women, respectively.
In early July 2016, an adult female resident of Miami-Dade County (patient A) sought treatment at a local hospital with fever, rash, and arthralgia. Serum and urine specimens, which were collected 3 days after symptom onset, were positive for Zika virus by rRT-PCR. Less than 1 week later, an adult male resident of Broward County (patient B) sought treatment for fever, rash, and arthralgia. Zika virus infection was confirmed by rRT-PCR on a urine specimen and serum IgM by enzyme-linked immunosorbent assay (ELISA) (to minimize the potential for false positives, the Florida Department of Health protocol requires two positive results for index case identification). Investigation of both cases indicated no recent travel to or sexual contact with a recent traveler to an area with active Zika virus transmission, no association with household contacts who recently traveled, and no close personal contact with a patient with confirmed Zika virus infection. There were no epidemiologic links between the two patients, and their residences were separated by >10 miles. BG-Sentinel (Biogents AG, Regensburg, Germany) mosquito traps, designed for researchers, collected a limited number of Ae. aegypti and Ae. albopictus specimens around the patients' residences, and PCR testing of pooled mosquitoes for Zika virus was negative (Sharon Isern, Department of Biological Sciences, Florida Gulf Coast University, personal communication, 2016).
To identify additional evidence of local transmission, household contacts of patients A and B were interviewed regarding recent illness and travel, and specimens were requested for Zika virus testing. Among seven household contacts of the two patients, none reported symptomatic illness and only one had laboratory evidence of recent flavivirus virus infection (Zika virus IgM results and neutralizing antibodies for both Zika virus and dengue, indicating probable Zika virus infection). This person had moved from Haiti to Florida 1 month before onset of symptoms in patient A and was classified as having a travel-associated case of Zika virus disease.
To identify recent infections in the surrounding neighborhoods of patients A and B, systematic surveys were conducted of all households located within 150–300 meters (164–328 yards) of each patient's residence. In addition, an outdoor worksite near patient B's residence also was sampled; these areas were selected based on the typical flight range of Ae. aegypti.[4] Surveys were conducted at the end of July and consisted of urine specimen collection and a standardized questionnaire regarding general risk factors. Three visit attempts were made for each occupied residence. Children aged <5 years and persons with recent travel to an area with ongoing Zika virus transmission were excluded. Among 116 urine specimens collected from persons from 54 households and one worksite, all were negative for Zika virus by rRT-PCR. In addition, enhanced passive surveillance through syndromic surveillance, review of public health and commercial laboratory results, and notification by local health care providers did not identify any additional cases related to patients A and B.
Morbidity and Mortality Weekly Report. 2016;65(38):1032-1038. © 2016 Centers for Disease Control and Prevention (CDC)
