In a recent MPDN post about asymptomatic carriers of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which causes COVID-19 I noted that these people can be infected and infect others without ever knowing they are ill. This is particularly concerning because we have not had enough testing in the state (or the country for that matter) to know the incidence of these cases. It is also concerning because we are opening up businesses and many people do not take the most basic precautions to protect themselves and others, such as wearing a mask in public or practicing physical distancing. We are also seeing an influx of tourists in our state and have no way of knowing who has actually been tested or quarantined. Finally, there have been a variety of gatherings around the state and the country, such as the heavily televised campaign rally for the POTUS yesterday, in which masks were worn by very few, voices were loud, and people were crowded at an indoor location; conditions near ideal for spread from asymptomatic carriers.
This past week a scientific letter published in Nature Medicine about asymptomatic carriers raised more concerns about COVID-19 that have a lot of bearing on all of this. The cases were detected by the Chinese Wanzhou District Centers for Disease Control and Prevention (CDC), which conducted RT–PCR tests on 2,088 “close contacts under quarantine.” None of these people had symptoms in the two weeks prior to testing. This is especially relevant because in the U.S. the standard is to have people who have had a close contact with a sick person go into isolation for two weeks. If they develop no symptoms, they come out of isolation. In this study, a positive test was detected in 178 patients. All 178 were hospitalized and a variety of tests were conducted. All patients were followed for several weeks. Among these 178 cases, 37 (20.8%) remained asymptomatic. Within the 37 asymptomatic cases, the average age was 41 years, and 22 were female.
A younger average age is an interesting feature that might speak to the fact that younger people seem to do better with the virus if exposed. However, that might also lead people to a false sense of security. First, not all young people do so well. Many younger people (including children) with COVID-19 in our country have died or suffered a variety of serious illnesses. Second, these people might spread disease, even if they are not so sick. If one person infects two other people, and those two people infect two other people, it doesn’t take long for infection to grow to huge numbers. For another example of exponential growth, see this post.
It is important to understand a little about how the testing was done to understand a couple other concerns. Recall that polymerase chain reaction (PCR) is a test for genetic material. PCR looks for the genetic material of the organism when the COVID-19 test is done, and in that case the only way for one to have a positive test is if the organism is present (an infection). In this study, the amount of genetic material found in the 37 asymptomatic cases was compared against symptomatic cases and found to be the same. Similar to the prior post on asymptomatic cases, this tells us that viral shedding, or the amount of virus being emitted is probably about the same between symptomatic an asymptomatic people. (footnote)
The authors also reported that asymptomatic carriers were found to shed virus for a period of time longer than people with symptomatic disease. The average duration of viral shedding among these “silent spreaders” was 19 days, with a range of 15-26 days (versus an average of 14 days among symptomatic patients). This longer duration may be related to another finding in the study, that asymptomatic carriers in this report had a less robust immune response than people with symptomatic disease. This concept fits with the idea that much of the damage done to the body with severe cases is thought to be caused by an infected person’s own immune response. In other words, a person with a strong immune response to the virus might wind up severely ill, and if they survive, stop shedding virus faster than a person with a weaker immune response and fewer neutralizing antibodies. Also, asymptomatic people in the report had lower levels of pro- and anti-inflammatory cytokines. The so-called “cytokine storm” is implicated in progression to severe disease in symptomatic cases.
However, the longer duration of positive testing could have another meaning. Again, a positive PCR test means genetic material is present, but does not necessarily imply viral infectivity is still possible. It could be that after one has stopped being infectious a test could remain positive for a few days due to viral debris. It is known in many other viral infections that the immune system can neutralize viruses by damaging the outer envelope or aggregating virus particles. These acts prevent infection but do not destroy the nucleic acid, which degrades slowly over time. One example is measles virus RNA, which can be detected for up to 8 weeks after the clearance of infectious virus. As an analogy, if you thought there was a nest of hornets in your attic, and you had a test that picked up hornets, it might not distinguish between live hornets and the ones left behind after fogging the attic with hornet spray. It would take a while for the hornets to disintegrate.
Whatever the case, asymptomatic carriers reproduce and spread virus. Being in the presence of someone who is slowly emitting virus by talking or breathing is much less risky if that person is wearing a mask. It is also less risky if the encounter is kept brief, if you are wearing a mask also, and if are physically distanced at least 6 feet. Indoor environments are less dangerous if air is being circulated away from you to the outside (windows open, air exchangers, or negative pressure rooms).
So let’s close with a few words from the president yesterday. To paraphrase, he stated he had asked for COVID-19 is a “flu,” that testing to be slowed down in this country, because if you test, you find cases. He made a point that some cases are mild and should not have been counted. He stated that he had probably saved hundreds of thousands of lives by acting as quickly as he did. He was wrong on all counts, and several more I haven’t mentioned. What he said about COVID-19 so clearly illuminated his indifference to science and experts, failure to read daily briefings, inability to grasp or accept simple medical facts, and failure to lead in a health crisis. What he had to say, and the very fact that he brought so many people from all over the country together for an indoor rally where masks were not required, and where people who had to sign a waver stating they would not hold him liable if they caught COVID-19, was dangerous, and sent a very bad message about public health and his lack of concern for the wellbeing of even his own supporters. This came even after the deaths over 120,000 Americans during this pandemic, a number which is still growing.
We need a lot more testing to understand the incidence of asymptomatic cases, for contact tracing, isolation, and public health. We need leaders who, if they don’t understand what is going on, at least listen to experts, take their recommendations, and model the behavior in those recommendations. This comment is not about politics. It is about common sense and public health.
Until we have a vaccine or some reasonable intervention comes along we need to wear masks, practice physical distancing, wash our hands, stop touching our faces (unless the hands and the face are clean). Stay well, and follow the advice of the Maine CDC.
FOOTNOTE: We should note of course that coughing and sneezing emit huge numbers compared with talking or simple breathing. Still, the point is important, asymptomatic people can shed a lot of viral particles, and infect others.
