COVID-19 Asymptomatic and Rapid Antigen Testing

Prof Lisam Shanjukumar Singh *

 Testing for COVID-19 (File photo)
Testing for COVID-19 (File photo) :: Pix - TSE

Till 29th July 2020, the total number of persons infected with the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in the state is 2458. Out of them, 1653 persons have been recovered from the disease (COVID-19) while 805 persons are undergoing treatment. As per reports, a 56-year-old man succumbed to the disease at the Regional Institute of Medical Sciences (RIMS).

It is the first report of COVID-19 death in Manipur. One more death related to COVID-19 at RIMS on 30th July has been reported on social media (subjected to correction). The number of COVID-19 infected persons continues to rise in Manipur adding to the number of localities/Leikai declared as containment area.

At the same time, the number of deaths due to COVID -19 seems to increase. Among the people of Manipur, there is fear that community transmission in the state has begun.

Manipur was in the category of green zone for a long period after the two infected persons with the SARS-CoV-2, who have returned from outside the state recovered. Many people including so called experts started explaining why Manipur is not affected much by COVID-19. In many TV discussion, experts explained that because of food habits or fermented foods or UV radiation, the people of Manipur are protected against COVID-19.

A research can be done on the issue and scientific truth can be found out later. But it is not the time to convince the people that you are protected from COVID-19 because of food habits or fermented foods without scientific evidence. It was also said by experts on TV that people of Manipur should not be worried of the pandemic because no one has died because of COVID-19 in the state so far.

The question is “How many COVID-19 related deaths would set an alarm for us to start worrying?”

Recently, a doctor mentioned on a TV discussion (Impact TV Manung Hutna) that asymptomatic (not showing symptom of CODIV19) person infected with SARS-CoV-2 does not transmit the disease to other persons. However, the following selected recent case reports from around the world demonstrated that asymptomatic or pre-symptomatic persons infected with SARS-CoV-2 transmit the disease to other persons.

According to a case study (JAMA. 2020 Apr 14; 323,14: 1406"1407), an asymptomatic 20-yearold woman, lives in Wuhan and travelled to Anyang on January 10, 2020. As of February 11, she had no elevated temperature measured or self-reported fever and no gastrointestinal or respiratory symptoms, including cough and sore throat as reported or observed by doctors.

RT-PCR results showed that she was negative on January 26, positive on January 28. She transmitted the disease to 4 persons whom she met on 10 and 13 January. None of the patients had visited Wuhan or been in contact with any other people who had travelled to Wuhan except the woman. One person out of 4, developed fever and sore throat on January 17 and went to the local clinic for treatment.

The other 3 persons started developing fever and respiratory symptoms between January 23 and January 26 and were admitted to the hospital on the same day. All patients had RT-PCR test results positive for COVID-19 within 1 day.

It has been reported that a 53- year-old UK patient with an asymptomatic COVID-19 infection may have caused 11 infections [Gulland A. Could you be a coronavirus super spreader?. 2020 [EB/ OL],].

Another report pointed out that one asymptomatic person who experienced 19 days from contact with the source of infection to RT-PCR confirmation may have infected 5 people [Bai Y, Yao L, Wei T, Tian F, Jin DY, Chen L, et al. Presumed asymptomatic carrier transmission of COVID-19. Jama 020;323(14):1406e7].

These asymptomatic cases may have played a role in the transmission and therefore pose a significant challenge to infection control [Gao Z et al., A systematic review of asymptomatic infections with COVID-19, Journal of Microbiology, Immunology and Infection,].

Similarly, one asymptomatic child (aged 10 years) who had a history of travel to Wuhan from Shenzhen was described in the report about a family cluster of COVID-19. The child was diagnosed as an asymptomatic carrier by screening after other family members developed symptoms [Chan JF, et al.

A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: a study of a family cluster.Lancet. 2020;395:514-523]. On February 25, a case of COVID-19 transmission occurring in a prison in Rencheng district, Jining city, Shandong province was reported. On February 9, a man was released from prison and returned home. But he was informed to isolate himself because a prison officer was confirmed to have COVID-19 infection on February 14.

In order to avoid isolation and observation, the man absconded from his home. Later, it was confirmed that this man was an asymptomatic carrier, and his brother who had close contact with him became infected with COVID-19. The above case reports are examples of asymptomatic transmission.

Studies have reported that the viral load that was detected in the asymptomatic patients was similar to that in the symptomatic patients, which also theoretically suggests the potential transmission of asymptomatic patients [Zou L, Ruan F, Huang M, et al. SARS-CoV-2 viral load in upper respiratory specimens of infected patients. N Engl J Med. 2020;382(12):1177-1179, and Chen Y, et al. The epidemiological characteristics of infection in close contacts of COVID- 19 in Ningbo city[J/OL]. Chin J Epidemiol 2020:41].

If one conducts a thorough research on the COVID-19 infection in Manipur, there may be many good examples of asymptomatic transmission. Indeed, COVID-19 transmission through asymptomatic carriers is a challenge to containment [Xingxia Yu, and Rongrong Yang, Influenza Other Respi Viruses. 2020;14:474"475].

Researchers have hypothesised that salivary glands may function as potential reservoirs of SARS-CoV-2 in asymptomatic infected individuals [Xu J, Li Y, Gan F, Du Y, Yao Y. Salivary Glands: Potential Reservoirs for COVID-19 Asymptomatic Infection. J Dent Res. 2020:22034520918518].

ACE2 is an important receptor for COVID-19. Salivary gland epithelial cells express a high level of ACE2. The expression of ACE2 in minor salivary glands was higher than that in lungs which suggests salivary glands could be a potential target for COVID-19. In addition, SARS-CoV RNA can be detected in saliva before lung lesions appear. This may explain the presence of asymptomatic infections.

This suggests that COVID-19 transmitted by asymptomatic infection may originate from infected saliva [J. Xu, et. al. Salivary Glands: Potential Reservoirs for COVID-19 Asymptomatic Infection Journal of Dental Research 2020, Vol. 99(8) 989]. From the facts mentioned above, a doctor (expert) claiming on TV discussion that asymptomatic persons infected with SARS-CoV-2 does not transmit the disease to other persons is wrong and that is very dangerous proposition in the present situation of Manipur, as disseminating false information would aggravate misconception among the public.

The next important issue is the Rapid Antigen Testing (RAT) which has been in strategic use recently in Manipur. Indian Council of Medical Research (ICMR) has recommended the use of Standard Q COVID-19 Ag detection assay (antigen detection test) as a point of care diagnostic assay for testing under certain settings in combination with RT-PCR test.

The RAT is to detect a protein present at the outer cover of the SARS-CoV-2 (here the protein is called as antigen). In the testing kit antibody against the protein (antigen) is present. Antigen and antibody binding is very specific like a lock and a key, and the binding reaction which is called as agglutination reactions is very fast.

The agglutinated complex of antigen and antibody becomes insoluble and therefore can be detected easily by naked eyes if a dye is used. The testing can be done in 30 mins. If no virus is present in the sample, the agglutination complex will not be formed. Although it is very specific, sensitivity is low. A certain amount of antigen and antibody is required to form the agglutinated complex.

Unlike RT-PCR, there is no amplification step for the molecules to be detected. Becauseprotein can not be amplified, unlike RNA and DNA. Therefore, when amount of virus is low in the sample, no agglutination is formed or very little agglutination is formed which cannot be detected.

Therefore, the false-negative result is high in the case of Rapid Antigen Testing when the viral load of the patient is low. “ICMR has recommended that those found negative in the rapid antigen test should be definitely tested sequentially by RT-PCR to rule out infection, whereas a positive test should be considered as a true positive and does not need reconfirmation by RT-PCR test”.

It is also clearly written on top of the instructions provided by the manufacture of the rapid antigen testing kit (SD Biosensor) that “it is recommended to perform ANTIGEN TESTING WITHIN 6 DAYS after symptom onset, and ANTIBODY TEST FROM 7 DAYS after symptom onset”. Dr Nivedita Gupta from ICMR also told the Delhi High Court in a court case against Delhi Government that ICMR never said asymptomatic rapid antigen test negative persons should not undergo RT/PCR testing, it only said the symptomatic rapid antigen test negative patients be given priority.

Taking note of the ICMR stand, the court told the Delhi government that it has to “strictly” follow the guidelines on COVID-19 testing as issued by ICMR and not according to its own interpretation. The important point here is that the rapid antigen testing is not for asymptomatic persons.

Coming to the situation of Manipur, there are many questions to be answered. Whether the persons who found negative by the rapid antigen test are confirmed by RT-PCR?. If not the case, Manipur is on the verge of explosive rise in COVID-19 cases. If a person is an asymptomatic carrier but the viral load is not detectable by the rapid antigen testing, the result of the rapid antigen testing will show negative result.

When such persons are declared to be free from COVID-19 based only on the rapid antigen testing and set free without any care, what will be the situation in Manipur. A study can be done in the case of Manipur by conducting parallel testing of RT-PCR and RAT in a selected small population of Manipur so that the sensibility of the RAT may be determined.

It is high time for the state to educate itself and act without delay based on facts and scientific evidences rather than acting for a temporary solution basis.

* Prof Lisam Shanjukumar Singh wrote this article for Imphal Times
The writer is Head of Department of Biotechnology Department at Manipur University
The writer can be contacted at shanju(DOT)lisam(AT)manipuruniv(DOT)ac(DOT)in
This article was webcasted on August 02, 2020

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