Covid-19 Healthcare Challenge - what are asymptomatic carriers and are they contagious?

15th June 2020 by Asimina Pantazi


A week ago, Mary met five friends of hers in a park in central London. All of them had been social distancing for two months and they hadn’t presented any COVID-19 – related symptoms. Mary and her friends considered that disobeying the physical distancing rules was acceptable. Yesterday Mary presented a dry cough and high fever, both symptoms of COVID-19. She did the test and her results came 24 hours later: she was COVID-19 positive. But how?

One of the assumptions was that one of Mary’s friends was an asymptomatic carrier of the pathogen. By etymology, the word asymptomatic (prefix “a” + word “symptom”) means without symptoms.

An asymptomatic COVID-19 patient does carry the pathogen in his body, but does not express any of the symptoms. This may happen in two cases. First, the person may be undergoing the very early stages of the disease, the so-called early incubation period, and be “not yet symptomatic”.1 During this phase, although the person carries the virus, the immune reaction is not yet complete and therefore there are no symptoms. In fact, this case should be referred to as “pre-symptomatic”.1 Second, the person may never experience any symptoms throughout the total course of the viral infection. Since asymptomatic persons are not routinely tested, the prevalence of asymptomatic infection and detection of pre-symptomatic infection is not well understood.1

The epidemiological significance of asymptomatic infections is unclear.2 It is known that the transmission of SARS viruses occurs during the symptomatic period.3 However, with SARS-CoV-2 numerous asymptomatic infections were found among people in communities with confirmed patients, for example in the cases of the “Diamond Princess” and the Australian cruise ships.4,5 Furthermore, scientists followed a computational approach using normal breathing and coughing aerosol samples from asymptomatic carriers and estimated a high viral load.6 This may provide an explanation why there are frequent COVID-19 community transmissions from asymptomatic cases.

Although the exact degree of SARS-CoV-2 viral RNA shedding that confers risk of transmission is not yet clear1, a study from late May shows that the viral shedding from asymptomatic carriers is much lower vs symptomatic carriers.7 It is now generally acceptable that risk of transmission is greatest when patients are symptomatic, since viral shedding is greatest at the time of symptom onset and declines over the course of several days to weeks.1 However, in the lack of concrete data, whether asymptomatic SARS-CoV-2 carriers are contagious still remains controversial.2

How can a person find out if they are asymptomatic carriers? If for any reason you are suspecting you may be asymptomatic, there are a few measures you can take:

  • Self-isolate and advise the people living with you to self-isolate too for 14 days.8 You need to be considerate of the others and avoid spreading the disease in case you are contagious.
  • If you live alone, inform your family and close friends you are self-isolating and ask for their support when required.
  • Confirm your case with a COVID-19 antigen test. If more than 14 days have passed since you first suspected you had COVID-19, it may be more appropriate to ask for an antibody test, which measures the anti-SARS-CoV-2 antibody levels in your blood.8

Unfortunately, the NHS does not provide the above testing services to members of the public that are asymptomatic, therefore you would have to reach out to private providers.

In conclusion, it is important that all people follow the national regulations assuming that everyone is a carrier. The use of face covering, regular handwashing and physical distancing are generally advised, especially in countries with high number of cases. More importantly, hospital staff should wear strict respiratory protection when there is a chance to be in the same room with a suspected patient - whether symptomatic or not - especially if this was for a prolonged time.6

Given the uncertainty about the clinical profile of COVID-19, several countries are enforcing mass testing upon arrival at the airports from countries of high risk, to enable a safe entry beyond borders. Provision of regular testing followed by identification and tracing of asymptomatic cases would enable easing the lockdown measures and a safe return to normality. Last but not least, further research is crucial to help us understand the behaviour of the virus and the risk of transmission from asymptomatic carriers.

Disclaimer: the names and personal story are fictional.

References

1.     https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-guidance-management-patients.html [Accessed June 2020]

2.     Gao et al. 2020. Resp Med. doi: 10.1016/j.rmed.2020.106026

3.     Zeng et al. 2009. Biomed Environ Sci. doi: 10.1016/S0895-3988(10)60008-6

4.     Mizumoto et al. 2020. Euro Surveill. doi: 10.2807/1560-7917.ES.2020.25.10.2000180

5.     Ing et al. 2020. Thorax. doi: 10.1136

6.     https://www.medrxiv.org/content/10.1101/2020.04.27.20081398v1.article-info [Accessed June 2020]

7.   Jang et al. 2020. JAMA Netw Open. doi:10.1001/jamanetworkopen.2020.10182

8.   https://www.nhs.uk/conditions/coronavirus-covid-19/self-isolation-and-treatment/when-to-self-isolate-and-what-to-do/ [Accessed June 2020]


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