County Public Health Lab Busy Watching for Zika

Microbiologist Patrick Aziz prepares samples to test for Zika.

The virus is not dominating the national headlines at the moment. But the County of San Diego is continually working to protect the public from Zika.

Since the epidemic of the Americas began in Brazil in 2015, the County Health and Human Services Agency’s Public Health Laboratory has been very busy testing specimens of patients who traveled to Zika-impacted areas. More than 1,300 referrals have been tested in the lab, where each case is tested twice and sometimes three or four times to determine if the patient has or had Zika.

We are taking every measure to protect the public from Zika.

Wilma Wooten, M.D., M.P.H., County public health officer

“We are testing every case that shows possible symptoms of Zika to keep the disease from coming into our communities,” Wooten said.

When samples from a potential case come in, a test is conducted to determine if the patient still has the virus in the body. A second test is also conducted to see if the person has developed Zika antibodies, an indication that the person, while no longer contagious, was infected with Zika. When both tests come back negative, one and sometimes two additional antibody tests are conducted at a later time since it may take up to two to three weeks for antibodies to appear.

Some of the samples are also tested for dengue and chikungunya, since symptoms are similar and the viruses can be transmitted by the same mosquitoes, the invasive Aedes mosquitoes.

PH Lab-Zika TestingOf the people tested for Zika in San Diego, 1,083 cases were determined not to be Zika and 87 were confirmed or probable Zika cases. Furthermore, there were 23 dengue cases last year and two this year, to date. Also, there were six chikungunya cases last year and one, so far, in 2017. Updates on the virus are provided every Friday at the County’s Zika webpage.

All Zika, dengue and chikungunya cases reported locally have been travelers returning to San Diego from more than two dozen Zika-affected areas, including two who contracted the virus sexually and one transmitted through birth. To date, no invasive Aedes mosquitoes have been found in San Diego County or California carrying these diseases.

“We’re very busy,” said Brett Austin, County public health lab director, explaining that Zika tests are currently being conducted two to three times each week. “At the moment our primary focus is Zika because it can be a very tragic disease. We don’t want it to get established here.”

When a patient is believed to be still contagious with the Zika virus, the County HHSA Epidemiology Program immediately notifies the County Department of Environmental Health Vector Control Program, which in turn sends staff to see if there are Aedes mosquitoes present in the area where the patient lives. If the patient is confirmed to be contagious and there are Aedes mosquitoes present, Vector Control notifies residents in a roughly two-block area around the patient’s residence and conducts hand spraying to kill the mosquitos.

To date, of the 259 cases referred to the Vector Control Program for assessment, the County has only needed to conduct 10 hand sprayings to kill adult mosquitoes.

“If people come back infected with Zika and then they are bitten by invasive Aedes mosquitoes while they are infectious, there is the possibility the mosquitoes could pick up the infection and transmit it to someone else,” said County Department of Environmental Health Director Elise Rothschild, indicating that the closest locally transmitted Zika case was reported in Ensenada earlier this year. “Our primary goal is to avoid local transmission.”

In addition to Zika, dengue and chikungunya, microbiologists at the Public Health Lab can detect practically any organism, including avian flu, plague, norovirus, HIV, rabies, drug-resistant tuberculosis, and pandemic H1N1 influenza.

The Public Health Lab processes about 60,000 specimens and performs more than 80,000 tests each year. Also, the lab tests more than 1,500 water samples—drinking water, wastewater, and recreational water—per year.


José A. Álvarez is a communications specialist with the County of San Diego Communications Office. Contact