All antigen positive cases told to isolate
In an about-face, the San Antonio Metropolitan Health District is instructing its case investigators to advise those who lack symptomsofCOVID-19 but test positive in an antigen test to isolate and quarantine.
That’s a shift from last month, when case investigators were told to inform such patients that they were “not a case.” Those were Metro Health’s instructions despite the high accuracy of antigen positive test results, even in those without symptoms.
The policy had raised red flags for members of a Metro Health contact tracing work group. Mayor Ron Nirenberg called last week for antigen positive cases without symptoms to be counted as probable and investigated; Metro Health then tweaked the instructions to case investigators.
But the health authority still is not counting such patients as “probable” cases or opening public health investigations into their close contacts, as other major Texas cities — including Houston, Austin and Dallas — already do.
In San Antonio, case investigators are instructed to close each case and categorize it as “not a case,” a policy that some public health experts fear is downplaying the extent of COVID-19 in the community and hampering the city’s ability to tamp down the spread of the disease.
“Change ‘Closure Reason’ tab to ‘Not a Case,’” the new instructions read. “Do not inform the person that they are ‘Not a Case,’ this is for reporting purposes only. The individual may still be infectious, so please advise according to CDC guidelines.”
After meeting on Friday, the contact tracing work group — made up of public health experts who are advising Metro Health — voted to recommend that the health authority follow CDC guidelines in the way it treats antigen
positive patients without symptoms.
That would mean counting all antigen positive lab reports as “probable” cases; fully investigating them, regardless of whether the patient has symptoms; and informing the patient that they are a probable case, collecting their contacts and telling them to isolate for the rest of the contagious period.
In addition, the work group said contact tracing should be conducted for those close contacts.
Metro Health does open investigations into antigen positive patients if they have symptoms. The district includes those cases in its total COVID-19 case count, classifying them as “probable.”
The steering committee of the COVID-19 Community Response Coalition now must approve the work group's recommendations before Metro Health can adopt them. Formed in May, the coalition is led by Metro Health Director Colleen Bridger and Dr. Barbara Taylor, associate professor of infectious diseases at UT Health San Antonio.
Taylor was not available to speak Monday.
In a previous interview, Bridger dismissed the concerns of the work group as “a whole lot of ado about nothing,” arguing that the Food and Drug Administration has authorized the use of antigen tests only in people who have symptoms of COVID-19.
Last month, FDA spokesman Jim KcKinney said the reason for those limitations “is the risk of potentially missing cases” — not the risk of falsely detecting positive cases.
Positive antigen tests correctly identify the virus more than 99 percent of the time, according to the Centers for Disease Control and Prevention. They can identify infections within minutes by detecting proteins from the virus in secretions from the nose and throat.
Antigen tests are not as sensitive as PCR tests, so a negative result from an antigen test does not rule out an infection. Negative results from an antigen test may need to be confirmed with a PCR test, which looks for pieces of the virus in the nose or throat.
A positive antigen test, however, means the person likely has an active COVID-19 infection — even if they have no symptoms.
Experts say nearly half of those who get infected have no symptoms but are able to transmit the virus as socalled silent spreaders. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has said that 40 to 45 percent of people infected by the virus have no symptoms.
Investigating positive cases and tracing their close contacts are critical to slowing the spread of the virus in a community, although case investigators have struggled to reach many COVID-19 patients.
For each new COVID-19 case, a case investigator is assigned to call the patient and collect information on any close contacts. The investigators share that information with contact tracers, who warn the close contacts that they've been exposed to the virus and encourage them to get tested and to self-quarantine.
Last month, Dr. Joseph Petrosino, chairman of the Department of Molecular Virology and Microbiology at the Baylor College of Medicine in Houston, said that anyone who tested positive in an antigen test should be counted and traced as if they tested positive in a PCR test.
“Counting is important enough because your disease prevalence in the community is what dictates public policy on reopenings,” Petrosino said then. “If they're not even following up on positive antigen cases, then what's the point?”