The present study revealed changes in the AECOPD hospitalization rates and isolation rates of corresponding respiratory pathogens after the COVID-19 outbreak. The number of patients hospitalized with AECOPD decreased by approximately 44% compared with the number over the same period before the outbreak. Similar phenomena have been reported globally. In the United States, an analysis of the Veterans Affairs Corporate Data Warehouse, a national repository of electronic health records created during visits to all Veterans Affairs facilities, revealed a 48.4% decline in COPD admissions to Veterans Affairs hospitals after the outbreak8. In the United Kingdom, analysis of data from Public Health Scotland and the Secure Anonymized Information Linkage Databank of Wales revealed a 48% pooled reduction in AECOPD requiring hospital admission9. In Singapore, the monthly rate of acute COPD admissions decreased by more than 50% in the first 5 months (February–July 2020) after the outbreak10.
Decreases in AECOPD may be associated with reduced transmission of respiratory-associated pathogens. Most COPD exacerbations are caused by bacterial or viral infections3. Globally, the incidence of AECOPD and transmission levels of respiratory viruses simultaneously decreased11. The present study also showed that the overall detection rates of bacteria and viruses decreased after the outbreak, explaining the observed AECOPD reduction.
H. influenzae, M. catarrhalis, S. pneumoniae, and P. aeruginosa were commonly isolated from AECOPD patients in previous studies12. The most commonly detected viruses in such patients were rhinovirus, influenza A, and RSV13. As in a previous study,12,13 S. pneumonia and P. aeruginosa were the frequently identified bacteria, whereas influenza A and rhinovirus were the most common viruses, in the present study. H. influenzae, M. catarrhalis, and RSV were also detected in the present work.
Notably, we found that pathogen detection rates changed after the COVID-19 outbreak. The incidences of S. pneumoniae, H. influenzae, and all viruses except COVID-19 significantly decreased after the outbreak. Such changes have been reported worldwide. A previous study demonstrated significant and sustained reductions in invasive diseases caused by S. pneumoniae, H. influenzae, and N. meningitidis, beginning in early 20206. All viral detection rates have declined worldwide. The Centers for Disease Control and Prevention reported a 98% decrease in influenza activity, from a median of 19.34% to 0.33%, in the United States14. Southern Hemisphere countries (Australia, Chile, and South Africa) have also reported minimal influenza activity. Furthermore, the detection rates of RSV, rhinovirus, metapneumovirus, and parainfluenza virus have decreased4. Consistent with previous international reports, we found that the influenza detection rate substantially decreased from 10.4% to 1.0%.
The changes may be partly explained by the widespread introduction of COVID-19 lockdown policies. S. pneumoniae and H. influenzae are typically transmitted person-to-person via the respiratory route15. Respiratory viruses are transmitted in respiratory droplets and aerosols16. Therefore, widespread adoption of COVID-19 containment policies, such as social distancing and the use of face masks in public spaces, may have reduced the transmission rates of respiratory-related pathogens and COVID-19. The COVID-19 containment policies and relevant public information campaigns slowed the transmission of respiratory-related pathogens, thereby reducing AECOPD rates. Therefore, COVID-19 containment policies are effective in lowering AECOPD levels. Although long-term implementation of strict COVID-19-like containment policies is impossible considering the socioeconomic costs, the COVID-19 experience may aid the establishment of strategies to prevent AECOPD.
The S. pneumoniae and respiratory virus detection rates significantly declined, but the detection rates of P. aeruginosa and MRSA significantly increased, after the COVID-19 outbreak. Both P. aeruginosa and MRSA are associated with poor AECOPD outcomes17,18. In other studies, K.pneumoniae, P.aerusinosa, and MRSA were reported as strains causing colonization in COPD patients19-22. Additionally, approximately 20% of hospitalized COPD patients is colonized with MRSA18. These pathogens have the capacity to engage in chronic colonization; the corresponding numbers may be less affected by COVID-19 quarantine policies, compared with the numbers of other pathogens. Colonization precedes obvious clinical infection. Murphy et al23. reported that exacerbations caused by P. aeruginosa were more common in patients with advanced COPD compared with early COPD. The median predicted FEV1 of patients in the present study was 45% and almost half of the patients had a history of AECOPD, reflecting the severity of COPD. These results may explain the increased detection rate of P. aeruginosa after the COVID-19 outbreak.
MRSA is associated with adverse outcomes among patients with AECOPD. Narewski et al18. reported that COPD patients colonized with MRSA had longer hospitalizations, required longer courses of antibiotics, and was more likely to require intensive care. Additionally, persistent infection with MRSA in patients with cystic fibrosis was associated with a more rapid rate of decline in lung function24. Similarly, we found that MRSA infection was prognostic of mortality before and after the COVID-19 outbreak. COPD patients colonized with MRSA may require close attention.
The present work was a multicenter study including a large number of patients and we comprehensively evaluated the changes in pathogens infecting AECOPD patients before and after the COVID-19 outbreak. However, our study had some limitations. First, this was a retrospective work. Second, we could not evaluate the pathogen status of AECOPD patients after COVID-19 containment policies were completely lifted. It remains unclear whether the observed changes have persisted since easing began. In May 2023, the World Health Organization declared that the COVID-19 public health emergency was over. Thus, an additional study is needed. Third, changes in healthcare utilization by patients with non-COVID-19 conditions during and after the outbreak may have affected pathogen detection rates25-27. In the present study, the numbers of patients transferred from other hospitals and discharged to other hospitals after treatment both decreased during and after the outbreak. These findings may be related to difficult transfer between hospitals during lockdown, which could have impacted the pathogen detection rates.