Patients with higher prior antibiotic use are more likely to experience severe Covid-19 outcomes after infection, including hospitalisation and death, a new study led by the University of Manchester has shown.

When infected with Covid-19, the chances of dying from complications due to Covid-19 is 1.34 times higher in patients with the most exposure to antibiotics than those without antibiotic exposure.

The research, published in eClinical medicine, is the first to explore how the severity of Covid-19 is affected by prior antibiotic use.

The UK team of scientists behind the work say the findings should act as a warning against the overuse of antibiotics.

Using the NHS OpenSAFELY platform, which enabled the researchers to look at electronic health records across primary and secondary care, the team examined data from 670 000 patients infected with Covid-19 between February 2020 and December 2021. The patients were reviewed for Covid-19 outcomes and divided into five groups based on the frequency with which they had taken antibiotics three years prior to infection.

Each group was further split based on the number of different antibiotics a patient used, giving the researchers an understanding of how the frequency and diversity of antibiotic use affect the body’s response to a Covid-19 infection. Of the sample, 98,420 patients were admitted to hospitals, 22,660 died, and 55 unique antibiotics were prescribed.

Patients with more frequent antibiotic exposure in the past three years were more likely to experience severe Covid-19 outcomes, including admission to hospital and death within 30 days.

The odds of being hospitalised due to a Covid-19 infection were 1.8 times higher for those with the highest history of antibiotic use and the most diversity of antibiotic use. Using a range of antibiotics was more likely to be associated with Covid-19 hospital admission, and using a larger range of antibiotic types was associated with more severe consequences of  Covid-19 upon hospital admission.

Professor Tjeerd van Staa, a principal investigator from the University of Manchester, said: ‘Our study has provided evidence that patients with high prior antibiotic use were more likely to experience severe Covid-19 outcomes. In addition, we also found an association between the number of different prior antibiotic types and Covid-19 related hospital admission.’

The researchers suggest this may be because frequent antibiotic use can increase the likelihood of patients being infected with viruses or bacteria, leading to an increased susceptibility to adverse consequences of infection.

Professor Van Staa added: ‘The literature shows that antibiotic treatment might alter gut microbiota, which can impact metabolic and immune function. While in most situations, gut microbiota will recover after stopping an antibiotic course. Frequent antibiotic use may affect the resilience of gut microbiomes more seriously.’

The researchers suggest that antibiotic guidelines should outline the possible adverse consequences of the overuse of antibiotics, and personalised patient leaflets could highlight these risks and the risks of the patient’s bacteria developing resistance to antibiotics.

Co-principal investigator Dr Victoria Palin from the University of Manchester said: ‘Common infection guidelines in England, as developed by the National Institute for Health and Care Excellence, focus on the treatment of the first infection episode. They do not provide guidance around repeated antibiotic use and a patient’s risk of developing resistance.’

She added: ‘There needs to be more awareness of the impact of long-term antibiotic exposure and its adverse outcomes. We would discourage regular and indiscriminate prescribing of these drugs for self-limiting infections.’

A version of this article was first published by our sister title Nursing in Practice