Likely order of Covid symptoms depends on coronavirus variant: Study

The most likely order of symptoms that patients with COVID-19 experience is different for different variants of the SARS-CoV-2 virus, according to a study.

The researchers from the University of Southern California in the US wanted to know whether the order of COVID-19 symptoms varied in patients from different geographical regions or with various patient characteristics.

Identifying order of symptom onset of infectious diseases might aid in differentiating symptomatic infections earlier in a population thereby enabling non-pharmaceutical interventions and reducing disease spread, they said.

The study, published in the journal PLOS Computational Biology, used modelling approach to predict symptom order in a set of 373,883 cases in the US between January and May 2020.

The most likely symptom order differed between the initial outbreak in China -- where fever most often preceded cough, and nausea or vomiting was a common third symptom -- and the subsequent spread to the US.

In the US, cough was most likely to be the first symptom, and diarrhoea was a more common third symptom.

By analysing additional data from Brazil, Hong Kong and Japan, the team showed that the different order of symptoms was associated not with geographic region, weather, or patient characteristics, but with SARS-CoV-2 variants.

The presence of the D614G variant in an area -- which was predominant in the US in early 2020 -- was associated with a higher likelihood of cough being the first COVID-19 symptom experienced by patients.

As Japan shifted from the original Wuhan reference strain to the D614G variant, symptom order shifted as well, the researchers said.

The study authors hypothesise that the increased transmission of D614G could be linked to the symptom order.

"These findings indicate that symptom order can change with mutation in viral disease and raise the possibility that D614G variant is more transmissible because infected people are more likely to cough in public before being incapacitated with fever," they added.