Months before Houston experienced its spike in COVID-19 cases, it was already a proving ground for measures to prevent SARS-CoV-2 transmission among health care workers. A recent study analyzed infection rates among COVID-facing and non-COVID-facing workers to better understand asymptomatic infection and guide prevention strategies.

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The study, “Prevalence of SARS-CoV-2 Infection Among Asymptomatic Health Care Workers in the Greater Houston, Texas, Area,” published in JAMA Network Open®, looked at 2,872 self-reported asymptomatic individuals, made up of 2,787 heath care workers at Houston Methodist and 85 community residents, between March 11 and April 19, 2020. Each person was tested via one of three cross-validated reverse transcriptase–polymerase chain reaction assays.

Overall, 3.9% tested positive for SARS-CoV-2. Among clinical health care workers, the study found a 4.8% difference in positive test results between COVID-facing and non-COVID-facing health care workers—5.4% in COVID-19 units and 0.6% in non–COVID units. Within COVID-19 units, results varied by job category, with 5.7% of clinicians, 5.3% of nurses, 6.5% of allied health workers, 3.6% of support staff and 6.5% of administrative or research staff testing positive.

Watch a recent episode of the AMA COVID-19 daily video update with insights from an emergency medicine physician on the pandemic’s spike in Houston.

There are clues in the data

The timing of the study has strong implications for the findings, one of the study’s authors noted.

“I think our knowledge of PPE was limited back then,” said Roberta L. Schwartz, PhD, chief executive officer of Houston Methodist Hospital. “If you remember, during this time there were not recommendations to be masked up 100% of the time. There were offstage areas—both within the hospital and even between the hospital and the parking lot—where many staff were not masked.”

This resulted in a curious pattern of infections.

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“We had clusters of maybe 15 people from one small emergency department testing positive,” Schwartz said. “And then we figured it out: It was the break room. Those who tested positive were, say, a security guard, a patient access rep, a patient care assistant, a nurse, a physician—who had no commonality except for the break room.”

In fact, none of the nonclinical health care workers or community residents had positive test results. Nonclinical health care workers were located in buildings with separate entrances, as well as separate heating, ventilation and air conditioning systems. Their workspaces also had lower population density due to the hospital’s remote working policies.

Armed with these findings, Houston Methodist has been able to implement changes that have driven down positive test results.

“Our tracing efforts to date suggest that the positive asymptomatic employees have community-acquired infection,” she said. “Our COVID-19 positive rate is currently under 1% in both COVID-facing and non-COVID facing units.”

Learn more from the AMA about a 10-step road map for ensuring PPE access during the pandemic.

A short list of must-haves

“Studies have demonstrated that uniform masking, hand hygiene and some type of eye protection are essential for health care workers,” Schwartz said. “And that has to be held in onstage areas and offstage areas—wherever we cannot guarantee a level of physical distancing. We need to be very clear that these are must-haves at this point.”

In addition, testing might need to be routinized.

“While it's hard to argue for surveilling the entire population every 14 days, in those areas where you have people coming into contact with infected patients in any type of less than ideal protection, you should be doing more surveillance,” Schwartz said.

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The study’s limitations include convenience sampling from a single health care system and a small, homogenous sample of community residents.

Where to look for official guidance

The AMA has developed a COVID-19 resource center as well as a physician’s guide to COVID-19 to give doctors a comprehensive place to find the latest resources and updates from the CDC and the World Health Organization. 

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