Story tips from Johns Hopkins experts on Covid-19

The COVID-19 pandemic has sparked heightened awareness of cleaning and disinfecting procedures in many industries. Health care facilities have long been familiar with protocols for disinfecting tools and equipment, and now, scientists are studying methods to improve these procedures, making them safer and more efficient for patients and health care workers.

At Johns Hopkins, biomedical engineer Jeff Siewerdsen and radiologist Mahadevappa Mahesh are investigating the use of UV light to disinfect the inner bore of CT scanning machines, a cramped space that is exposed to exhaled particles from patients and is difficult to reach by manually wiping it down.

The UV light being studied is not the typical beam of sunshine that falls to the earth. Those rays are mostly UVA rays, which tend to cause skin cancer and other problems. Siewerdsen and Mahesh are studying UVC rays, which can eliminate a high proportion of SARS-CoV-2 virus from hard surfaces.

They attached a UVC lamp to the bed inside the bore of a CT scanner and found that the UV light wiped out 99.9999% of SARS-CoV-2 virus particles in three to five minutes. A summary of the results was published Nov. 18, along with a video abstract, in the Journal of Applied Clinical Medical Physics.

The lamp used in the study cost $105; however, they did not study the longevity of the lamp. The researchers also note that there may be crevices in the CT scanner that are not reachable with the UV light.

If the UVC procedure for CT scanners proves useful, the process could be used in addition to the manual wipe down of CT scanners, improve the safety of personnel and patients, and applicable to many health care facilities around the globe.

Note: Exposure to UVC light could harm health. UVC lamps should not be used without proper training and safety precautions. Read more information from the FDA.


Media Contact: Michael E. Newman,

Repeated testing for SARS-CoV-2, the virus that causes COVID-19, has become common practice during the ongoing pandemic, especially when there is a strong suspicion that a person is infected with, or has been exposed to, the pathogen. Molecular diagnostics are the standard means for detecting the presence of SARS-CoV-2 genetic material (RNA), with negative assays from two consecutively collected respiratory specimens more than 24 hours apart and no symptoms being the benchmark for when a patient can end quarantine and return to normal activities.

However, recent research has shown that while SARS-CoV-2 RNA can be detectable with molecular testing for weeks after the onset of symptoms, it doesn't necessarily denote the presence of infectious virus particles. In a medical records study looking at results from nearly 30,000 COVID-19 tests over a two-month period, a team led by researchers at Johns Hopkins Medicine and the Johns Hopkins Bloomberg School of Public Health gained significant insight into when virus detection also may indicate contagiousness.

The findings were published online Oct. 27 in the journal Clinical Infectious Diseases.

From March 11 to May 11, 2020, the researchers evaluated the results of repeated polymerase chain reaction (PCR) diagnostic tests for SARS-CoV-2 RNA in 29,686 nasopharyngeal swabs. The PCR assay is very specific and detects the viral RNA by accumulation of a fluorescent signal. The number of times it takes to get a positive signal is called the cycle threshold (Ct), with a low Ct score indicating a large amount of SARS-CoV-2 RNA and a high one just the opposite.

"We also placed a portion of the specimens in cell cultures to see whether or not live virus particles would grow," says Heba Mostafa, M.B.B.Ch., Ph.D., assistant professor of pathology at the Johns Hopkins University School of Medicine and co-senior author of the study. "In that way, we could compare the Ct values with actual virus recovery in the lab to see when detected virus also was infectious virus."

The researchers found that the average Ct value associated with cell culture growth of SARS-CoV-2 was 18.8. They also observed viral growth from specimens collected up to 20 days after the first positive result, mostly in patients who were symptomatic for COVID-19 at the time of specimen sampling. Sequencing of the entire genome from RNAs collected in the first and subsequent tests provided evidence that the same virus was seen throughout. Positive tests following negative ones had Ct values higher than 29.5 and were not associated with observed virus growth in culture.

"Our findings support the theory that low Ct values in SARS-CoV-2 diagnostic tests are associated with recoverable virus, and that RNA detection in repeated tests may indicate someone who continues to be infectious with persistent symptoms," Mostafa says. "However, additional studies are needed to truly determine if Ct values and cell cultures can be used together to make clinical decisions, develop diagnostic strategies and identify those most likely to spread SARS-CoV-2."

"Defining the window of time in which a COVID-19 patient can transmit the virus can help drive more effective isolation practices," adds Andrew Pekosz, Ph.D., professor of microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health and co-senior author of the study.

Johns Hopkins Medicine