Patients with rheumatic and musculoskeletal diseases face substantial risk from severe COVID-19 infections, but this risk has diminished over the course of the pandemic, according to new research from the US.

Some earlier reports found increased risk of respiratory failure requiring mechanical ventilation, as well as hospitalisation, in patients with rheumatic and musculoskeletal diseases than in the general population. Improvements in testing, supportive care, and treatments have been seen in the general population since early 2020, but such temporal trends have not previously been specifically examined in patients with those rheumatologic diseases.

“It is important to understand these temporal changes given that historical comparator groups are increasingly used to gauge the efficacy of potential treatments for COVID-19 and to inform patients with rheumatic and musculoskeletal diseases and their health-care providers of the current risks,” wrote study authors led by Dr April Jorge, of Massachusetts General Hospital in Boston.

The researchers compared 2,811 patients with rheumatic and musculoskeletal diseases diagnosed with COVID-19 in the first 90 days of the pandemic with 5,729 diagnosed in the second 90 day period. The study was published in Lancet Rheumatology.

In an exposure score matched analysis, the risk of hospitalisation was lower in the late cohort (32.4%) than in the early cohort (45.4%), with a relative risk of 0.71 (95% CI, 0.67-0.76). The same trend was seen with regard to the risk of intensive care unit admission (7.9% vs. 14.3%), mechanical ventilation (3.6% vs. 9.1%), acute kidney injury (13.8% vs. 20.7%), and renal replacement therapy (0.6% vs. 1.2%).

The risk of death was 4.5% in the late cohort, compared with 9.3% in the early cohort, for a relative risk of 0.48 (95% CI, 0.39-0.60).

When restricted only to patients who were hospitalised, there was a lower risk in the late cohort of a composite endpoint including ICU admission, mechanical ventilation, and death (30.7% vs. 41.3%), with an RR of 0.74 (95% CI, 0.67-0.83).

“This finding is probably multifactorial, due to increased testing capacity allowing for detection of milder cases, improved supportive care, and improved treatments,” the authors wrote.

“Despite the temporal improvements we observed in our study, there continues to be a considerable risk of morbidity and mortality from COVID-19 among patients with rheumatic and musculoskeletal diseases.”

A EULAR report from June 2020 found no increased risk either for contracting COVID-19 or for worse outcomes once contracted. However, a study from later in the year focused on rare autoimmune rheumatic diseases, and it did show that the risk of death during the pandemic rose more for these patients than in the general population.