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Infectious Diseases

Updated 30 June 2020

What researchers learned from Italy's Covid-19 outbreak: Many cases didn't show the usual symptoms

A study on an Italian outbreak epicentre revealed that just about a third of confirmed cases were symptomatic.

  • A Covid-19 study from Italy found almost a third of confirmed cases symptomatic with respiratory issues and/or a fever of 37.5 degrees Celsius or above.
  • Only 2.7% of the cases required hospitalisation or resulted in death - but the chances of symptoms increased with age.
  • Those under 20 had the least risk of developing symptoms - but could still spread the virus. 


The role of asymptomatic spread in the pandemic has been a hot topic lately, especially after the World Health Organisation's comments - and retraction - over the probability of Covid-19 positive people with no symptoms passing it unknowingly on to others. 

A new study from Italy - one of the original epicentres of the pandemic - however, may show some insight into the prevalence of symptoms among those infected with the coronavirus. 

They released a pre-print of their findings in arXiv which still needs to be peer-reviewed. 

Researchers focused on almost 5 500 contact cases in Italy’s Lombardy - an area hard-hit by Covid-19 - of which just more than half tested positive for the virus. 

READ: Top WHO official backtracks on comments that asymptomatic spread of Covid-19 virus is 'rare'

"Quantifying the proportion of SARS-CoV-2 infections that do not show recognisable symptoms is still an important missing piece in the puzzle of the ongoing pandemic," writes the authors of the paper. 

Focusing only on the symptoms of respiratory issues like coughing and shortness of breath and a fever of more than 37.5 degrees Celsius, they found that only 31% of the positive cases had these symptoms. 

These are some of the most well-known symptoms for the coronavirus. 

The probability of symptoms, however, rose in accordance with age, and about 74% of infected cases under the age of 60 did not develop these symptoms. 

For those under 20 years of age it was 18.1%, while those over 80 the probability of symptoms skyrocketed to almost 65%.

This still made it possible for them to pass on the virus, as viral loads between symptomatic and asymptomatic people were found to be the same. 

Only 2.7% of total cases were critical - where patients were hospitalised or died - and that the majority of these critical patients were male. 

This could be crucial information as many countries like South Africa require symptoms like coughing and fever to qualify for getting tested due to limited resources. 

WATCH: Coronavirus: What does asymptomatic mean?

The study, however, doesn't mention the loss of taste and smell - a symptom that most experts now agree is a major early indicator of a coronavirus infection

These participants - while a large group - also come from an area with an above-normal infection rate and can't be directly correlated to the general population. 

But the researchers believe this data is useful for planning for future outbreaks. 

"The quantification of the risk of critical disease upon infection can inform estimates from transmission models and help ensure the sustainability of health system in terms of supplies, human resources, equipment and beds required at different intensities of care."

Image credit: Canva