After a summer of anxiety over Zika, the volume of testing for the virus has dropped significantly, data from the athenahealth network shows.
Since August, the Centers for Disease Control and Prevention has reported no new local transmission of Zika in Wynwood, Florida, the Miami neighborhood that saw the nation’s first homegrown cases. The volume of people returning from vacations to Zika-affected areas has also tapered off.
As a result, the number of Zika tests ordered nationally on athenahealth’s network decreased by more than 42 percent in the month since a mid-August peak. Over the same period in Florida, testing fell by 49 percent.
“This is around the time when you would expect things to settle down,” says Maia Majumder, a biostatistician and epidemiologist at HealthMap, a Boston Children’s Hospital project that tracks disease outbreaks. If recent numbers out of Zika-affected Colombia are any indication, she notes, the number of suspected cases will continue to drop and testing should stabilize at low levels for the rest of the year.
According to athenahealth data, 75 percent of Zika tests this season were ordered by OB/GYNs and primary care physicians. The vast majority of those tests — 87 percent — went to women, 93 percent of them between the ages of 19 and 44.
Men ages 19 to 44, the second-largest group to receive Zika tests, represented 9 percent of total tests, even though Zika can be sexually transmitted.
Indeed, for patients nationwide — even those trying to conceive after recent travel to Zika-afflicted areas — Zika tests have been hard to come by.
Public health specialists note that the CDC has encouraged providers to be selective about testing to prevent a backlog at labs. The agency also has prioritized testing for all pregnant women who have visited areas with active Zika transmission or live in Miami-Dade, Florida, whether or not they show symptoms of the virus.
“The CDC didn’t want to be swamped with tests, and they had to protect that resource and…focus the test on the patient where the public health interest was the greatest,” says William Schaffner, M.D., an infectious disease specialist and the head of preventive medicine at Vanderbilt University Medical Center. “The CDC was wise to do that from a public health, as well as a limited resource, point of view.”
Tracking a virus
Despite a focused testing strategy, it’s difficult to tell how many patients were actually infected with Zika, due to delays at the labs and challenges in interpreting results.
“One concern is whether or not the average primary care provider or obstetrician knows how to interpret the results of the test in the clinical context,” Schaffner says. “Since it’s a new phenomenon and information is coming out daily, it’s not something you learned in medical school or residency.”
But according to the CDC, 899 pregnant women nationwide showed lab evidence of a possible Zika infection. As of October 19, all of the locally acquired Zika cases nationwide — 137 — were reported in Florida.
While trend lines have flattened out with cooler weather, Schaffner says, U.S. travel to Central America, South America, and the Caribbean, where exposure could put more patients at risk, will determine future virus transmission and testing volumes. In Brazil, which was roiled by Zika last season, summer begins again in December.
“Everything in the U.S. has to do with how frequently people in those countries come to the U.S. or how frequently people from the U.S. go to those countries and come back,” says Schaffner. “Those of us in public health can’t take our eye off the ball.”
Chelsea Rice is a staff writer for athenaInsight.