• epidemiology
• COVID-19
• autoimmune diseases

We read with interest the article by Bower et al detailing the impact of the COVID-19 pandemic on mortality and morbidity among patients with rheumatic diseases (RDs).1 Though Bower et al reported that the risks of severe COVID-19-related outcomes among patients with RD, such as increased risk of hospitalisation and death, were largely proportionate to those in the general population and explained by comorbidities, risks of severe COVID-19-related outcomes were still increased among patients with RD.1 Indeed, in a separate cohort of inpatients with systemic lupus erythematosus and concomitant SARS-CoV-2 infection, almost one-fifth required intensive care unit admission.2 Outside the pandemic setting, however, common respiratory viral infections (RVIs), including influenza, still remain a significant cause of morbidity and mortality among patients with RD. Increased influenza incidence has been reported among patients with RD,3 and various anti-RD therapies are associated with increased frequency of RVIs.4 Public health measures, such as influenza vaccination, are hence recommended for RVI prevention in patients with RD,5 though most RVIs are not vaccine-preventable. The COVID-19 pandemic provided the impetus for introduction of unprecedented, community-wide public health measures targeted against SARS-CoV-2 transmission. Such measures may also potentially reduce transmission of common RVIs among vulnerable populations, including patients with RD.

In Singapore, a Southeast Asian city state, various public health interventions, including universal masking and social distancing, were implemented from February 2020 onwards.6 Given the success of these measures in limiting community transmission, lockdown measures implemented in April 2020 were lifted by June 2020, with the reversal of most social-distancing measures by December 2020. However, compulsory mask wearing in public continues to be maintained. At our institution, the largest tertiary hospital, community containment of COVID-19 meant that services were fortunately not overwhelmed, unlike other centres that experienced closure of rheumatology services as part of SARS-CoV-2 containment, with patients postponing care due to fear of transmission.7 Inpatient rheumatology services continued throughout the pandemic, with telemedicine augmenting outpatient consults.8 We evaluated trends in concomitant RVIs among inpatient rheumatology admissions over an unbroken 1-year period during the pandemic, compared with the preceding 2 years. From January 2018 to February 2021, all rheumatology admissions with a PCR-proven RVI in the same admission were identified. Prepandemic, patients with symptoms of upper respiratory tract infection (URTI) had samples tested for 16 common RVIs (including influenza) via multiplex PCR. During the pandemic, all inpatients with URTI were additionally tested for SARS-CoV-2 as well as common RVIs as part of our institution’s containment strategy for COVID-19.9 The rates of admissions with PCR-proven RVI prepandemic and postpandemic were compared using the incidence rate ratio method.

We observed a significant and sustained reduction in concomitant RVIs among rheumatology admissions during the pandemic (figure 1). The incidence rate of PCR-proven RVI was 4.7 cases per 1000 admissions (4 cases and 851 admissions) during the pandemic, compared with 24.1 cases per 1000 admissions pre-pandemic (36 cases and 1494 admissions); the decline was statistically significant (incidence rate ratio=0.19, 95% CI=0.05 to 0.54, p=0.005). Influenza accounted for a minority of PCR-proven RVI (17.5%, 7/40). This remarkable decline was noted despite increased testing, likely due to heightened vigilance for respiratory symptoms. While almost one-third (26.1%, 222/851) of admissions were tested for RVIs, prepandemic, only 15.3% (229/1494) of admissions were correspondingly tested (OR=1.94, 95% CI=1.58 to 2.40, p<0.001). Over a 9-month period from May 2020 to January 2021, zero RVI was encountered among rheumatology inpatients, an observation unprecedented in the preceding 2 years. During the pandemic, no patients with RD on follow-up at our institution developed COVID-19.

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Figure 1

Rates of RVIs among rheumatology inpatients at a Singaporean tertiary hospital, before and during the COVID-19 pandemic. RVI, repiratory viral infection.

A sustained reduction in admissions with PCR-proven RVIs among patients with RD coincided with widespread adoption of public health measures during a pandemic, including universal masking and social distancing. These reductions were sustained for more than 6 months after the lifting of lockdown and persisted even after the reversal of most social-distancing measures. While the single-centre nature of our observations restricts generalisability, the complementary role of simple preventive measures such as wearing of face coverings and social distancing in mitigating RVIs among those living with RD and in receipt of immunosuppression deserves further investigation, particularly as a majority of RVIs observed were not vaccine-preventable.