The percentage of people in Bexar County testing positive for the coronavirus decreased to 6 percent, officials said Monday, providing key evidence that local conditions have improved since a spike in July.

The positivity rate fell from 6.8 percent from the previous week and is the lowest it has been since the number of cases began to climb in June. The statewide positivity rate is 7.9 percent. 

Public health experts pay close attention to the positivity rate – the percentage of people tested for the novel coronavirus with positive results – because a high percentage of positive tests suggests additional cases remain undiagnosed and more people need to be tested.

The positivity rate is the closest measure of the true prevalence of COVID-19 throughout the community, said Dr. Anita Kurian, San Antonio Metropolitan Health District’s assistant director, on Monday. “When the positivity rate reaches 5 percent, it means there is no wide, rampant, ongoing transmission happening.”

The positivity rate in Bexar County, which Metro Health calculates weekly, was at just 3.6 percent at the end of May. It peaked during the second week of July, reaching just over 24 percent, according to Metro Health data. 

The positivity rate in a community also is used to determine how much testing should be available to residents, Kurian said.

Metro Health has the capacity to test at least 7,200 people per day, which is 100 more tests than were available in mid-July when the positivity rate was at its peak. At the time, city-run test sites were only testing people with COVID-19 symptoms.

Now that the positivity rate has declined, demand for testing is not as high, Kurian said, but testing is open to anyone regardless of symptoms.

Metro Health uses the Harvard Institute for Global Health’s suggested metrics when looking at COVID-19 and its spread throughout the county. The institute suggests that for a population of 2 million, at least 8,200 coronavirus tests per day should be available to the community. 

While Bexar County is slightly under that capacity, Kurian said the demand for testing at this point doesn’t warrant an increase in testing capacity. That’s because the progress and warning indicators such as hospitalizations and the amount of time it takes for the number of new coronavirus cases to double, are trending downward. 

“We may not be testing 8,200 people every day, but even among those we are testing, we are not finding a high rate of infection,” Kurian said.

Kurian said that while health officials have speculated about why Bexar County isn’t seeing high demand for testing, it’s not because they aren’t recommending it.

“I think we are just at a point where it isn’t as widespread throughout the community, which is a good thing,” she said.

Dr. Anita Kurian, Metro Health’s assistant director of communicable disease, works from a COVID-19 response center the City established at the Alamodome in July. Credit: Scott Ball / San Antonio Report

The World Health Organization recommends that an area’s positivity rate should be below 5 percent for at least two weeks before easing virus-related restrictions including limitations on restaurants and in-person schooling.

Once a community reaches the 5 percent zone for the positivity rate, it means mitigation efforts – social distancing, wearing masks, washing hands regularly, and staying home when sick – can be considered effective, Kurian said.

Kurian said the positivity rate is “still the best measure we have” to determine how widespread the coronavirus is in the community, even though its accuracy could be affected by the same person being tested more than once within a given time period. For example, a patient admitted to a hospital is tested repeatedly until he or she tests negative and is discharged, and all those results would be used in calculating the county’s positivity rate.

Bexar County’s positivity rate is just one indicator that the outbreak is subsiding locally. Four of the seven progress or warning indicators outlined by the COVID-19 transition team are in the green or “safe” zone. Officials say it is too soon to tell whether the Labor Day weekend or the return to campus of some students will cause a spike in cases, but it will become clear in the data reported Friday or Monday.

Gov. Greg Abbott said last month that bars could potentially reopen if the statewide positivity rate remains below 10 percent for an extended period of time. 

Kurian said that the biggest concern right now is that there might a spike in cases among young people and adults in their 20s who might not be taking the risk of the virus seriously, which caused the post-Memorial Day spike in cases and an additional increase following the Fourth of July. 

“All we can do is remain hopeful that people continue to follow the guidelines set by public health experts, because that is what we know is working,” Kurian said. “There is still a lot more we do not know about this virus than we do know.”

Roseanna Garza reports on health and bioscience for the San Antonio Report.