The Sun reports that a new study has found that “coronavirus patients are most infectious when they have mild symptoms”.

This claim could be misleading, as this small study didn’t compare how infectious people are when they have severe or mild symptoms.

The researchers took regular throat swabs and other samples from 9 patients in Germany with coronavirus. The patients had all had close contact with people with COVID-19, so they were tested early. Their symptoms were generally mild.

The researchers tested for both the genetic material from the virus (the standard test) and also for live virus. They showed that live virus was present in patients’ mouths, noses and throats in the first week of showing symptoms, but not after this. This suggests that people with coronavirus are more infectious in the first week after starting to show symptoms than they are later on.

The research does reinforce the importance of self-isolating as soon as you develop symptoms, and continuing to do so for 7 days, even if your symptoms are mild.

 

Where did the story come from?

The news is based on a recently published study of 9 patients who were diagnosed with coronavirus at one hospital in Germany this January. They all had contact with known COVID-19 patients and were diagnosed once they showed symptoms by testing swabs from their mouths or noses and throats for genetic material from the novel coronavirus.

What is the basis for the claim?

All of the patients had relatively mild symptoms. In most cases (7 out of 9 patients) a cough was one of their initial symptoms.

The researchers took regular repeat swabs and other body fluid samples from the patients to assess where the virus was present in the body, and at what levels. This continued until they could not detect the virus any longer (up to about 28 days).

These standard tests look for genetic material from the virus, but do not show for certain that live virus is present which could infect other people. Therefore the researchers also tested whether live virus was present in the samples. They showed that there were differences between tests for genetic material and the live virus (meaning infectivity).

Overall the research found:

  • The levels of the virus genetic material in swabs from the nose and mouth or throat were very high in the first 5 days of symptoms and decreased after that. There was detectable virus genetic material in the swabs into the second week after symptoms developed.
  • In most of the patients, it appeared as though the levels of the virus genetic material in the throat had already peaked by the time they first showed symptoms.
  • Live virus (that is, a virus that had the potential to infect others) was identified in the first week of symptoms from the swabs from the nose, mouth and throat and also sputum (saliva and mucus from the respiratory tract). After day 8 the researchers were no longer able to find live virus in these samples. This was despite still detecting high levels of the genetic material of the virus.
  • While virus genetic material was isolated from samples of poo, the researchers never managed to isolate any live virus from it.

 

What do trusted sources say?

Though small, this type of study is important for getting a better idea of when the virus is infectious. Policymakers will review this type of research as it accumulates to decide whether to update their strategies on how best to combat the virus.

The symptoms of coronavirus to look out for are high temperature or a new, continuous cough. UK Government advice is that people experiencing these symptoms, however mild, should stay at home and self-isolate for 7 days after symptoms start. If a person still has a high temperature after this time then they should continue to self-isolate until this returns to normal.

Social distancing measures and good hand hygiene will reduce the risk of people becoming infected or infecting others i.e. transmission if they unknowingly have the virus.

Analysis by EIU Healthcare, supported by Reckitt Benckiser

 

Citation

1.     Wölfel et al. Virological assessment of hospitalized patients with COVID-2019. Nature 2020 (Unedited manuscript published online 1 April 2020). https://www.nature.com/articles/s41586-020-2196-x

Reading list

1.     NHS Website. Symptoms and what to do: Coronavirus (COVID-19). Last reviewed 3 April 2020. https://www.nhs.uk/conditions/coronavirus-covid-19/symptoms-and-what-to-do/ (Accessed 6 April 2020)

2.     Public Health England. Stay at home: guidance for households with possible coronavirus (COVID-19) infection. Updated 24 March 2020. https://www.gov.uk/government/publications/covid-19-stay-at-home-guidance/stay-at-home-guidance-for-households-with-possible-coronavirus-covid-19-infection (Accessed 6 April 2020)