Experts say the prevalence of the virus may be higher than expected.
Asymptomatic carriers of COVID-19 may be spreading the disease without knowing it, but to what extent? According to new data published in JAMA, the rate of coronavirus infection in different parts of the United States may be much higher than anyone thinks.
Since January, it has been recommended that states report all confirmed cases of the new coronavirus to the Centers for Disease Control and Prevention (CDC); However, there may be more than 10 times more coronavirus infections than have been documented. Many people with positive antibodies, or suspected markers of previous infection, may not have had symptoms, so they could have spread the virus without knowing it.
The study is “corroborating other smaller previously conducted studies” showing that “the infection was much more widespread than we thought,” said John Brownstein, an epidemiologist, professor of biomedical informatics at Harvard Medical School and director of innovation at Boston Children’s Hospital.
The latest CDC estimate is that about 40% of infections come from people who don’t show symptoms. This means that people who are asymptomatic carriers of the virus can play an important role in community transmission (the spread of the virus through an unknown source in a particular area).
The agency’s most recent analysis included 10 cities and states in the United States, many of which have high infection rates. Some regions, such as Missouri, had an estimated number of cases that was 13 times greater than reported, but in other areas, such as New York City, the difference between infections and reported cases actually decreased over time, possibly suggests an improvement in testing ability. .
The concept of widespread testing, even for those who are asymptomatic, has been proposed as a tool to more accurately document infection rates. Countries like Iceland, which have implemented aggressive testing strategies and had the highest test rate per capita in the world, have successfully contained the viral spread, possibly through mass testing. Still, skeptics argue that increases in both the false negative rate (not detecting the virus when it is present) and the false positive rate (not detecting the virus when it is absent) would cause more harm than good.
And despite a higher prevalence of coronavirus cases in the population, “We cannot draw any conclusions about herd immunity from these data,” Brownstein said.
Herd immunity, the concept that a large enough portion of the community is immune to disease to stop dead, is the goal of many health experts during a pandemic.
Brownstein said that “the total number of people who have been infected is still low,” so “we are going to see many more cases” before the virus is contained or there is a vaccine. Furthermore, the results of several recent clinical trials suggest that a potential vaccine is still many months away.
The study researchers analyzed samples of people who had routine blood tests or were admitted to hospitals from March to May in 10 cities and states in the United States. However, during this time period, many people who may have visited their health care providers for routine tests or elective procedures probably chose to stay home due to the pandemic, and only those who were sickest ventured to the hospital. Therefore, the blood samples included in the study may not have been representative of the general population.
Despite this limitation, Brownstein believes that this study will still help us “better understand the community burden of COVID-19.” But even the numbers captured by these researchers may “underestimate the true prevalence of the disease,” he added.
Several recent scientific studies have assumed that after infection, people, especially those with mild or symptom-free symptoms, may have antibodies that begin to drop after just two to three months. Therefore, we may still have more to learn about what percentage of the population is actually infected with the virus at any given time, and the CDC data can only capture people who have recently been infected.
Additionally, with more undocumented infections, the case fatality rate (the proportion of people with coronavirus dying from it) may be lower than the estimated death rate, which is currently 3.7% in the US But experts say only time will help reveal the true death rate. The good news is that as we see improvements in care, better treatments, and eventually a vaccine, the death rate may continue to decline.
The only way “we are really going to get out of this pandemic is by wearing masks, social distancing” and following other measures established by the CDC, Brownstein said, “especially for those who are infected and asymptomatic.”
Shantum Misra, MD, is a senior internal medicine resident at Dartmouth-Hitchcock Medical Center and a contributor to the ABC News Medical Unit.
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