AccuWeather interviewed experts, including pathologists who have analyzed the virus, who say SARS-CoV-2 is susceptible to heat, light, and humidity, while others study weather patterns for their predictions
AccuWeather, as it watched the outbreak of SARS-CoV-2, the novel coronavirus that causes COVID-19, wanted to know what effect that warmer spring temperatures might have on curbing the spread of the virus. There is a good reason to ask this question. As microbiologists, infectious disease doctors, and primary care physicians know, the typical start and end to every flu season is well-documented and closely watched.
As SARS-CoV-2 ravages countries around the world, clinical pathologists and microbiologists debate whether it will subside as temperatures rise in Spring and Summer. Recent analyses suggest it may indeed be a seasonal phenomenon. However, some infectious disease specialists have expressed skepticism.
CNN reported that Nicholls was part of a research team which reproduced the virus in January to study its behavior and evaluate diagnostic tests. Nicholls was also involved in an early effort to analyze the coronavirus associated with the 2003 SARS outbreak involving SARS-CoV, another coronavirus that originated in Asia.
“Sunlight will cut the virus’ ability to grow in half, so the half-life will be 2.5 minutes and in the dark it’s about 13 to 20,” Nicholls told AccuWeather. “Sunlight is really good at killing viruses.” And that, “In cold environments, there is longer virus survival than warm ones.” He added, “I think it will burn itself out in about six months.”
The graphic above, created by John Nicholls, MBBS Adel, FRCPA, FHKCPath, FHKAM (Pathology), Clinical Professor of Pathology at the University of Hong Kong, shows “the temperate zone where the major SARS-CoV-2 hotspots have appeared so far. The variation from year to year, in this case, is minimal; however, meteorologists would typically use the 30-year normal data for this type of analysis.” (Caption and graphic copyright: AccuWeather/John Nicholls.)
Can Weather Predict the Spread of COVID-19?
Other researchers have analyzed regional weather data to see if there’s a correlation with incidence of COVID-19. A team at the Massachusetts Institute of Technology (MIT) found that the number of cases has been relatively low in areas with warm, humid conditions and higher in more northerly regions. They published their findings in SSRN (formerly Social Science Research Network), an open-access journal and repository for early-stage research, titled “Will Coronavirus Pandemic Diminish by Summer?”
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The MIT researchers found that as of March 22, 90% of the
transmissions of SARS-CoV-2 occurred within a temperature range of three to 17
degrees Celsius (37.4 to 62.6 degrees Fahrenheit) and an absolute humidity
range of four to nine grams per cubic meter. Fewer than 6% of the transmissions
have been in warmer climates further south, they wrote.
“Based on the current data on the spread of [SARS-CoV-2], we
hypothesize that the lower number of cases in tropical countries might be due
to warm humid conditions, under which the spread of the virus might be slower
as has been observed for other viruses,” they wrote.
In the US, “the outbreak also shows a north-south divide,”
with higher incidence in northern states, they wrote. The outliers are Oregon,
with fewer than 200 cases, and Louisiana, where, as of March 22, approximately
1,000 had been reported.
There’s been a recent spike in reported cases from warmer
regions in Asia, South America, and Africa, but the MIT researchers attribute
this largely to increased testing.
Still, “there may be several caveats to our work,” they
wrote in their published study. For example, South Korea has been engaged in
widespread testing that includes asymptomatic individuals, whereas other
countries, including the US, have limited testing to a narrower range of
people, which could mean that more cases are going undetected. “Further, the
rate of outdoor transmission versus indoor and direct versus indirect
transmission are also not well understood and environmental related impacts are
mostly applicable to outdoor transmissions,” the MIT researchers wrote.
Even in warmer, more humid regions, they advocate “proper
quarantine measures” to limit the spread of the virus.
The New York Times (NYT) reported that other recent studies have shown a correlation between weather conditions and the incidence of COVID-19 outbreaks as well, though none of this research has been peer reviewed.
Why the Correlation? It’s Unclear, MIT Says
Though the MIT researchers found a strong relation between
the number of cases and weather conditions, “the underlying reasoning behind
this relationship is still not clear,” they wrote. “Similarly, we do not know
which environmental factor is more important. It could be that either
temperature or absolute humidity is more important, or both may be equally or
not important at all in the transmission of [SARS-CoV-2].”
Some experts have looked at older coronaviruses for clues. “The coronavirus is surrounded by a lipid layer, in other words, a layer of fat,” said molecular virologist Thomas Pietschmann, PhD, Director of the Department for Experimental Virology at the Helmholtz Center for Infection Research in Hanover, Germany, in a story from German news service Deutsche Welle. This makes it susceptible to temperature increases, he suggested.
However, Pietschmann cautioned that because it’s a new
virus, scientists cannot say if it will behave like older viruses. “Honestly
speaking, we do not know the virus yet,” he concluded.
Epidemiologist and virologist Joseph Fair, PhD, MPH (above), Special Advisor for Ebola, USAID, and Research Professor at Texas A&M University, said that sunlight might be a bigger factor than temperature or humidity. “It really doesn’t have anything to do with the warmth, but it has to do with the length of the day and the exposure to sunlight which inactivates the virus through UV light,” he told NBC News. “The science is still out,” he said. “We can assume this will follow typical other coronavirus cases,” but “everyone in the scientific and public health community expect it to be back in the fall and we expect to be in this for quite some time.” (Photo copyright: Texas A&M University.)
Marc Lipsitch, DPhil, Professor of Epidemiology and Director of the Center for Communicable Disease Dynamics at the Harvard T.H. Chan School of Public Health, is skeptical that warmer weather will put the brakes on COVID-19. “While we may expect modest declines in the contagiousness of SARS-CoV-2 in warmer, wetter weather, and perhaps with the closing of schools in temperate regions of the Northern Hemisphere, it is not reasonable to expect these declines alone to slow transmission enough to make a big dent,” he wrote in a commentary for the center.
How should pathologists and clinical laboratories in this country prepare for COVID-19? Lipsitch wrote that Influenza does tend to be seasonal, in part because cold, dry air is highly conducive to flu transmission. However, “for coronaviruses, the relevance of this factor is unknown.” And “new viruses have a temporary but important advantage—few or no individuals in the population are immune to them,” which means they are not as susceptible to the factors that constrain older viruses in warmer, more humid months.
So, we may not yet know enough to adequately prepare for
what’s coming. Nevertheless, monitoring the rapidly changing data on COVID-19
should be part of every lab’s daily agenda.
At present, medical laboratories are collecting blood specimens for testing by authorized public health labs. However, clinical laboratories should prepare for the likelihood they will be called on to perform the testing using the CDC test or other tests under development.
“We need to be vigilant and understand everything related to the testing and the virus,” said Bodhraj Acharya, PhD, Manager of Chemistry and Referral Testing at the Laboratory Alliance of Central New York, in an exclusive interview with Dark Daily. “If the situation comes that you have to do the testing, you have to be ready for it.”
The current criteria for determining PUIs include clinical features, such as fever or signs of lower respiratory illness, combined with epidemiological risks, such as recent travel to China or close contact with a laboratory-confirmed COVID-19 patient. The CDC notes that “criteria are subject to change as additional information becomes available” and advises healthcare providers to consult with state or local health departments if they believe a patient meets the criteria.
Bodhraj Acharya, PhD (above), is Manager of Chemistry and Referral Testing at the Laboratory Alliance of Central New York. In an exclusive interview with Dark Daily, he stressed the importance that medical laboratories be prepared. “We need to be vigilant and be active and understand everything related to this virus and the testing. That’s the role of clinical laboratory scientists, to be ready because this can become a pandemic anytime. It can spread and tomorrow the CDC could announce it is disseminating the test to designated laboratories.” (Photo copyright: Laboratory Alliance of Central New York.)
Test Kit Problems Delay Diagnoses
On Feb. 4, the FDA issued a Novel Coronavirus Emergency Use Authorization (EUA) allowing state and city public health laboratories, as well as Department of Defense (DoD) labs, to perform presumptive qualitative testing using the Real-Time Reverse Transcriptase PCR (RT-PCR) diagnostic panel developed by the CDC. Two days later, the CDC began distributing the test kits, a CDC statement announced. Each kit could test 700 to 800 patients, the CDC said, and could provide results from respiratory specimens in four hours.
However, on Feb. 12, the agency revealed in a telebriefing that manufacturing problems with one of the reagents had caused state laboratories to get “inconclusive laboratory results” when performing the test.
“When the state receives these test kits, their procedure is to do quality control themselves in their own laboratories,” said Nancy Messonnier, MD, Director of the CDC National Center for Immunization and Respiratory Diseases (NCIRD), during the telebriefing. “Again, that is part of the normal procedures, but in doing it, some of the states identified some inconclusive laboratory results. We are working closely with them to correct the issues and as we’ve said all along, speed is important, but equally or more important in this situation is making sure that the laboratory results are correct.”
During a follow-up telebriefing on Feb. 14, Messonnier said
that the CDC “is reformulating those reagents, and we are moving quickly to get
those back out to our labs at the state and local public health labs.”
Above is a picture of CDC’s laboratory test kit for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). CDC is shipping the test kits to laboratories CDC has designated as qualified, including US state and local public health laboratories, Department of Defense (DOD) laboratories, and select international laboratories. The test kits are bolstering global laboratory capacity for detecting SARS-CoV-2. (Photo and caption copyright: Centers for Disease Control and Prevention.)
Serologic Test Under Development
The current test has to be performed after a patient shows
symptoms. The “outer bound” of the virus’ incubation period is 14 days, meaning
“we expect someone who is infected to have symptoms some time during those 14
days,” Messonnier said. Testing too early could “produce a negative result,”
she continued, because “the virus hasn’t established itself sufficiently in the
system to be detected.”
Messonnier added that the agency plans to develop a serologic test that will identify people who were exposed to the virus and developed an immune response without getting sick. This will help determine how widespread it is and whether people are “seroconverting,” she said. To formulate this test, “we need to wait to draw specimens from US patients over a period of time. Once they have all of the appropriate specimens collected, I understand that it’s a matter of several weeks” before the serologic test will be ready, she concluded.
“Based on what we know now, we believe this virus spreads
mainly from person to person among close contacts, which is defined [as] about
six feet,” Messonnier said at the follow-up telebriefing. Transmission is
primarily “through respiratory droplets produced when an infected person coughs
or sneezes. People are thought to be the most contagious when they’re most
symptomatic. That’s when they’re the sickest.” However, “some spread may happen
before people show symptoms,” she said.
The virus can also spread when people touch contaminated surfaces and then touch their eyes, nose, or mouth. But it “does not last long on surfaces,” she said.
Where the Infection Began
SARS-CoV-2 was first identified during an outbreak in Wuhan, China, in December 2019. Soon thereafter, hospitals in the region “were overwhelmed” with cases of pneumonia, Dr. Acharya explained, but authorities could not trace the disease to a known pathogen. “Every time a new pathogen originates, or a current pathogen mutates into a new form, there are no molecular tests available to diagnose it,” he said.
So, genetic laboratories used next-generation sequencing, specifically unbiased nontargeted metagenomic RNA sequencing (UMERS), followed by phylogenetic analysis of nucleic acids derived from the hosts. “This approach does not require a prior knowledge of the expected pathogen,” Dr. Acharya explained. Instead, by understanding the virus’ genetic makeup, pathology laboratories could see how closely it was related to other known pathogens. They were able to identify it as a Betacoronavirus (Beta-CoVs), the family that also includes the viruses that cause SARS and Middle East Respiratory Syndrome (MERS).
This is a fast-moving story and medical laboratory leaders are advised to monitor the CDC website for continuing updates, as well as a website set up by WHO to provide technical guidance for labs.
