Millions of people worldwide may have long-term smell or taste problems as a result of Covid-19, with women more likely to be affected, a study suggests.
About 5% of adults infected with the coronavirus may develop long-lasting changes to their sense of smell or taste, according to the research published in the BMJ.
With more than 550m confirmed Covid-19 cases to date, it means there may be long-term smell deficiencies for 15 million people and taste problems for 12 million (with an unknown overlap of those suffering both) for at least six months after an infection.
Given the devastating effect that loss of smell and taste can have on quality of life and wellbeing, this will have a huge impact on global health, the team of international researchers say.
Loss or change of sense of smell or taste can lead to “severe distress”, they say, and they call for health systems to be better prepared to support people who often feel “isolated” when dismissed by clinicians.
Daily activities such as smelling coffee and testing the flavour of food can become “disgusting and emotionally distressing”, experts say.
The study reviewed data from 18 studies involving 3,699 patients. The researchers used modelling to estimate how many people go on to suffer from altered taste or smell for at least six months after a Covid-19 infection.
They concluded that an estimated 5.6% of patients have smell dysfunction for at least six months and 4.4% have altered taste.
Women were less likely to recover their sense of smell and taste than men, and patients with greater initial severity of smell loss and those with nasal congestion were less likely to recover their sense of smell.
One female patient told researchers that she had yet to recover her sense of smell 27 months after her initial infection.
The researchers acknowledge several limitations to the research. The studies analysed varied in quality and relied on self-reporting, though they say this “may overestimate recovery, suggesting that the true burden of olfactory dysfunction is even greater.”
They say that while most patients are expected to recover their sense of smell or taste within the first three months, “a major group of patients might develop long-lasting dysfunction that requires timely identification, personalised treatment and long-term follow-up.”
Prof Danny Altmann, a professor of immunology at Imperial College London, who was not involved with the research, said: “This is a strong and important study, alerting us once again to the difficulties inherent in charting the scale of long-term damage caused by Covid-19.
“The authors conducted a rather rigorous meta-analysis across several cohorts, modelling the time to recovery of taste and smell. It goes without saying that problems with taste and smell are non-trivial for quality of life.
“This is part of a wider discussion about how we assess and address the persistent changes collectively termed long Covid. Studies such as this alert us to the hidden burden out there of people suffering with persistent symptoms but perhaps not having thought it worth contacting the GP on the assumption there wouldn’t be much to be done.”