Surprisingly, the prevalence of chronic respiratory disease among patients with SARS and COVID-19 appears to be lower than among the general population [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C6]6]. This is not the case for other chronic diseases and leads us to hypothesise that lung disease, patients’ behaviour or, more likely, their treatment may have some protective effect. Sadly, patients with underlying lung disease who develop COVID-19 and are hospitalised have worse outcomes, with a case fatality rate of 6.3% compared to 2.3% overall in China [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C7]7]. These individuals may have less reserve to cope with the pulmonary effects of severe infection or their immunopathological abnormalities may make them more susceptible to developing pulmonary inflammation and ARDS.

ICS, alone or in combination with bronchodilators, are used extensively in the treatment of asthma [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C8]8], and combined with bronchodilators have a role in the management of some patients with COPD [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C9]9]. There are a number of paradoxes about their effects on viral infections and exacerbation rates which are relevant when considering ICS use during the COVID-19 pandemic. ICS use in asthma and COPD is associated with an increased risk of upper respiratory tract infections [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C10]10, 11]. In people with COPD, ICS use is associated with a higher prevalence of pneumonia [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C12]12] and a change in the lung microbiome, although not a change in respiratory virus detection [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C13]13]. The evidence in asthma is less clear cut, but at least one observational study has shown an increased risk of pneumonia or lower respiratory infection [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C14]14]. In vitro studies have suggested that corticosteroids may impair antiviral innate immune responses [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C15]15, 16] and that ICS use leads to delayed virus clearance [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C17]17]. Other studies, however, have shown normal responses in patients on ICS [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C18]18]. It is important to note that most studies have been carried out with rhinovirus and there may be differences in the response to other viruses.

Conversely, there is evidence to suggest that taking ICS may be beneficial in dealing with virus infections, specifically those due to coronavirus. Pre-treatment of human respiratory epithelial cells in vitro with budesonide, in combination with glycopyrronium and formoterol, has inhibitory actions on coronavirus HCoV-229E replication and cytokine production [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C19]19]. Furthermore, early, not yet peer-reviewed data, suggest ciclesonide blocks SARS-CoV-2 RNA replication in vitro [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C20]20] and inhibits SARS-CoV-2 cytopathic activity [[url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236828/#C21]21], which may be of great relevance to reducing the risk of developing of COVID-19 in response to SARS-CoV-2 infection or reducing the severity of the disease.

A third possibility is that therapies used by patients with chronic respiratory diseases can reduce the risk of infection or of developing symptoms leading to diagnosis. It is important to note that, at most, only around half of patients with COPD in China take treatments that are standard in Europe and North America,6 but up to 75% of people in China with asthma use inhaled corticosteroids.7Furthermore, in in-vitro models, inhaled corticosteroids alone or in combination with bronchodilators have been shown to suppress coronavirus replication and cytokine production.8, 9Low-quality evidence also exists from a case series in Japan, in which improvement was seen in three patients with COVID-19 requiring oxygen, but not ventilatory support, after being given inhaled ciclesonide;10 however, no control group was used and it is not known whether these patients would have improved spontaneously. Yet, the possibility that inhaled corticosteroids might prevent (at least partly) the development of symptomatic infection or severe presentations of COVID-19 cannot be ignored. By contrast, a systematic review on the use of systemic corticosteroids to treat SARS, once established, showed no benefit but possible harm