Written by: Dr. Yuzuru Anzai
I summarized the recent topics on novel corona virus. This article does not represent the opinion of JMSA or any other organization.
Testing of COVID-19
The test which has been utilized so far in the US is a RT-PCR of SARS-CoV-2 itself. The specimen is obtained with a nasopharyngeal swab. Since this virus is an RNA virus, it is first converted to DNA and then amplified by PCR. This will detect the presence of virus and as a test, it is considered to be highly accurate. However, the swab has to have virus particles for the test to pick it up. The problem is that the virus often resides deeper than the swab can reach, resulting in false negatives. Therefore, the sensitivity of the RT-PCR is considered to be only 60-70%.
On 4/20, New York State began testing the antibody against SARS-Cov-2. There are IgM antibodies, which appears shortly after the infection, and IgG which are detected later and last longer. The presence of antibody indicates a history of infection. This will give us a more accurate number of the people who have been infected by this virus and make it possible to calculate the real fatality rate. It may also show the presence of immunity. Often antibodies fight against the antigen (in this case a virus) and protect the body. Even though we do not yet have clinical evidence that humans can acquire immunity against this virus, many experts think it is very likely based on animal data and also data with other coronaviruses. There have been reports of patients who tested positive a second time despite previously testing negative suggesting recovery from COVID-19, but many experts speculated that these negatives tests were false negatives.
On 4/23, governor Cuomo discussed initial antibody test results which showed almost 14% of NY State residents had antibodies. In New York City, the hardest hit city in US, COVID cases are confirmed in less than 2%. The total number of infected people is undoubtedly higher because people with mild symptoms are not even tested. Still this number was higher than expected. Washington University estimates that at the end of the first wave of infection, only 3% of US population will be infected, leaving 97% of US citizens vulnerable to the infection. This raised the concern for second and third wave of infection. However, if more people are already infected, it is possible that the next wave is not as bad as the one we are experiencing.
At the same time these data need to be interpreted with caution. Let’s talk about sensitivity and specificity. Sensitivity is the percentage of the people with disease who test positive, and specificity is the percentage of the people without disease who test negative. The antibody tests are a mixed bag and some of them are not reliable. The NYS website said that the specificity of the tests they are using is 93-100%, indicating that the test is accurate.
However, it is not as simple as it looks. Let’s just assume a sensitivity of 90% and specificity of 95%, which are good numbers for a test. If the prevalence of the disease is 10%
(10% of the people are infected), 10 out of 100 people have the infection. Of these 10 people, the test will correctly identify 9 to be positive. For the other 90 people without infection, 5% of them will have positive results (5% of 90 people ), meaning about 5 people are falsely positive. This will result in 14 total positives, matching governor Cuomo’s number. However, of these 14 positives, 5 are false positives (36% of the positive patients). This is because the performance of the tests is influenced by the prevalence. There has been discussion of sending people with positive antibodies back to work. However, the potential for significant false positives is one of the reasons why this decision needs to be implemented with caution.
Can pets transmit novel coronavirus? (Updated on 4/30)
On 4/6, it was reported that a tiger in the Bronx Zoo tested positive for COVID. Recently there has been a few reports of cats infected with this virus as well as a dog. This brought some anxiety to pet owners. Can their pet get infected or transmit the infection? I also read that SARS (close to the virus causing Covid-19) was transmitted from bats through civets (they are sometimes called civet cats but they are not cats) in China that people eat, thus is not applicable to normal house pets.
A new report in Journal Science said viral replication was observed in cats and ferrets, and they are susceptible to infection whereas SARS-CoV-2 replicated poorly in dogs, and not in chickens, pigs and ducks. (Shi et.al Science 4/8/2020). In this paper they demonstrated airborne transmission of the virus between cats by placing two cats in separate cages. This sounds a little scary but website of CDC states that there has not been a case that a pet transmitted infection to human. They do say social distancing applies to pets as well. They recommend your dog not to interact with non-family members or other dogs outside of the household, and to avoid a facility like a dog-run. We do see many dogs playing with each other in Central Park, but apparently it is not ideal. They also recommend to keep your cats indoors and not to let them interact with other people who are not family members.
American Veterinary Medicine has more detailed information about this topic on their website. For example, they address a question like “Do we need a wash a dog after we take him for a walk? Can dog hair transmit the virus?”
In summary, they say it is very unlikely that you get an infection from dog hair. Even though it has been reported that the novel coronavirus can survive on non-porous surface such as metal or plastic for a few days, it is unclear if you get an infection by touching these surfaces. Primary mode of transmission is considered to be from human to human. Dog hair or leash has a porous surface where the virus gets inactivated more quickly.