Effect of the Covid-19 pandemic on hospitalizations for non-Covid-19-pneumonia and exacerbations of chronic obstructive pulmonary diseases in Switzerland: comparison of national data between 2020/2021 and 2015–2019

Abstract

Background

Protective measures applied during the Covid-19 pandemic had a marked impact on the incidence of pneumonia. However, systematic data are lacking for hospitalizations for pneumonia and acute exacerbations of chronic obstructive lung diseases (AECOPD) not caused by SARS-CoV-2 in Switzerland. We aimed to compare the incidences of hospitalization for these entities between 2020/2021 and prepandemic years.

Methods

This retrospective study examined all nationwide hospitalizations for non-Covid-19-pneumonia and AECOPD listed as primary diagnoses based on ICD-10 codes between 2015 and 2021 in a publicly available hospitalization database of the Swiss Federal Statistical Office. Hospitalizations for acute coronary syndrome (ACS) and stroke were used as controls. Changes of monthly incidences of hospitalizations, length of stay (LOS) and mortality were compared between 2020/2021 and the average of 2015–2019.

Results

The incidences of hospitalizations for AECOPD and for pneumonia showed seasonal variations from 2015 to 2019 followed by significant and almost identical decreases in 2020/2021 (incidence rate ratio [IRR] 0.59, 95% CI: 0.45–0.77, p < 0.001, and IRR: 0.62, 95% CI: 0.52–0.74, p < 0.001, respectively). Hospital-mortality was slightly higher in 2020/2021 for AECOPD (2015–2019: 3.8%; 2020/2021: 4.2%, odds ratio [OR] 1.24, 95% CI: 1.07–1.44, p = 0.004) and for pneumonia (2015–2019: 4.5%, 2020/2021: 4.6%, odds ratio [OR] 1.17, 95% CI: 1.07–1.28, p < 0.001). Median LOS slightly decreased for AECOPD (2015–2019: 8 [IQR: 5–14] days; 2020/2021: 7 [IQR: 4–13] days, Wilcoxon test: p < 0.001) but slightly increased for pneumonia (2015–2019: 7 [IQR: 4–11] days; 2020/2021: 7 [IQR: 4–13] days, Wilcoxon test: p < 0.001). Throughout 2020/2021, there were no significant fluctuations observed in the incidences of ACS and stroke. (IRR: 0.98, 95% CI: 0.83–1.16, p = 0.810, IRR: 0.96, 95% CI: 0.81–1.14, p = 0.636, respectively).

Conclusion

The first two years of the Covid-19 pandemic showed a marked decrease in incidences in AECOPD and non-Covid-19 pneumonia hospitalizations in Switzerland. It is likely that this effect is associated with the society-based, at first vigorous, social distancing measures.

Introduction and background

The Covid-19 pandemic led to social distancing and general preventative measures up to nationwide lockdowns to reduce the spread of Covid-19. These also had an enormous impact not only on Covid-19 epidemiology but also greatly affected other communicable diseases [1]. In 2020, notifiable infectious diseases with droplet or airborne transmission showed a significant reduction in incidence in Switzerland [2]. Other non-notifiable infectious diseases, such as influenza, decreased dramatically during the pandemic, compared to previous years [3]. At the beginning of the pandemic, a large decrease in bacterial respiratory infections with Streptococcus pneumoniae, Haemophilus influenzae and Neisseria meningitidis was observed worldwide [4]. Prior to the spread of Covid-19, community-acquired pneumonia was a clinically and economically relevant burden [5]. In fact, pneumonia was present in 2.4% of total hospitalisations in Switzerland [6]. Although the incidence and deaths from chronic obstructive lung diseases (COPD) have been showing a downward trend for years, it is still the third leading cause of death worldwide according to the WHO and represents a relevant economic burden [7,8,9]. Different studies registered a lower incidence of acute exacerbations of chronic obstructive lung diseases (AECOPD) during the Covid-19 pandemic, for example in Hong Kong or England [10, 11].

However, there are no systematically analysed data on the effects of Covid-19 on the incidence of non-Covid-19- AECOPD and pneumonia in Switzerland.

Therefore, we aimed to analyse changes of the incidence of hospitalizations for AECOPD and pneumonia and their severity during the first two years of the Covid-19 pandemic compared to pre-pandemic years. We hypothesized that there would be significant decreases in hospitalizations with these diseases but due to changes in health-seeking behaviour greater clinical severity.

Methods and patients

In this retrospective study, all hospitalizations without age restriction for non-Covid-19 pneumonia and AECOPD that were coded as primary diagnoses based on ICD-10 codes (table) between 2015 and 2021 were extracted and analysed. Of note, ICD-10 pneumonia codes do not distinguish between community-acquisition and health-care acquisition. Age was provided with 5-year ranges. In addition, data on length of stay (LOS) and mortality as severity indicators were collected. To control for changes in general health-seeking behaviour, we also extracted data for acute coronary syndrome (ACS) and stroke as control diagnoses, for which we did not expect significant direct changes as a result of the pandemic. Data were retrieved from a public nation-wide database on hospitalizations hosted by the Swiss Federal Office for Statistics.

Ethical declaration

This database is accurately representative of all hospitalizations in Switzerland and had been used in the past for similar purposes [12]. As it provides fully anonymized information, written informed consent by patients and protocol approval by the institutional ethics committee and ethical approval are not necessary.

Statistical analysis

Among all hospitalizations between 2015 and 2021, we searched for the respective ICD-10 codes for hospitalizations with a primary diagnosis of AECOPD, pneumonia, ACS and stroke (Table 1) from 2015–2021. For AECOPD and pneumonia we removed those who simultaneously had a Covid-19 ICD-10 code. The monthly incidences of hospitalizations, LOS and mortality of patients with AECOPD, pneumonia, stroke and ACS were calculated based on the Swiss population at the end of the calendar year (2020, 2021; demographic data was obtained from Federal office of Statistics) and the mean of the Swiss population at the end of the respective calendar years (2015–2019) and compared between 2020/2021 and the average of 2015–2019. Considering that the pandemic did not exhibit significant escalation in Switzerland until March 2020, our analysis of the pandemic period commences from that particular month.

Table 1 ICD-10 codes used for the diagnostic groups

Acute coronary syndrome (ACS) and stroke were used as control groups (table). The in-hospital mortality and monthly incidence of hospitalizations with these primary diagnoses in 2020/2021 were calculated and compared with those during 2015–2019 as described above.

The evolution of the incidence rates of AECOPD, pneumonia, ACS and stroke over time was analysed using Poisson regression. The number of inhabitants living in Switzerland available on a yearly basis (denominator of the incidence rate) was used as offset values in the Poisson regression analysis in order to account for population size variations. The Covid-19 pandemics effect was tested. The results are reported as incidence rate ratio (IRR) and 95% CIs. All statistical analyses were performed using the R statistical software v. 4.2.1 (Vienna, Austria).

Results

Among the 10′170′501 hospitalizations between 2015 and 2021, there were 61′387 hospitalizations with a primary diagnosis of AECOPD, 148′097 hospitalizations with a primary pneumonia diagnosis, 150′198 hospitalizations with ACS and 131′541 hospitalizations with stroke. Demographic information of the study population is presented in Table 2. The incidences of hospitalizations for AECOPD and for pneumonia in 2015 to 2019 are showing seasonal fluctuations reaching a peak in the winter and a drop during summer months. These trends disappeared in early 2020 after the beginning of the Covid-19 pandemic which resulted in significant and similar decreases in 2020/2021 (incidence rate ratio [IRR] 0.59, 95% CI: 0.45–0.77, p < 0.001 for AECOPD, and IRR: 0.62, 95% CI: 0.52–0.74, p < 0.001 for pneumonia) (Figs. 1 and 2).

Table 2 Demographic characteristics of the study population

Fig. 1

Incidences of hospitalisations with AECOPD and pneumonia and due to any cause between 2015–2021. Monthly incidences of hospitalisations with AECOPD and pneumonia were depicted from 2015 until the end of 2021. Poisson regression was used to investigate temporal trends of incidences. Incidence rate ratios (IRR) were reported comparing monthly incidences in 2020/2021 with the incidence of the pre-pandemic years

Fig. 2

Incidences of hospitalisations with AECOPD, pneumonia, acute coronary syndrome and stroke during 2020 and the pre-pandemic years 2015–2019. Monthly incidences of AECOPD, pneumonia, ACS and stroke during 2015–2020. Showing the incidences per month for 2015–2019 in light blue, for 2020 in red. The dark blue line represents the average monthly incidence of 2015–2019

Hospital-mortality was slightly higher in 2020/2021 for patients with AECOPD (2015–2019: 3.8%; 2020: 4.2%, odds ratio [OR] 1.24, 95% CI: 1.07–1.44, p = 0.004), and for patients with pneumonia (2015–2019: 4.5%, 2020: 4.6%, OR: 1.17, 95% CI: 1.07–1.28, p < 0.001). Median LOS decreased slightly for AECOPD (2015–2019: 8 [IQR: 5–14] days; 2020/2021: 7 [IQR: 4–13] days, Wilcoxon: p < 0.001) but slightly increased for pneumonia (2015–2019: 7 [IQR: 4–11] days; 2020: 7 [IQR: 4–13] days, Wilcoxon test: p < 0.001).

The total number of hospitalizations also showed a significant decrease at the beginning of 2020. The number of all-cause hospitalizations recovered quickly and approached pre-pandemic levels towards late 2020 (IRR: 0.93, 95% CI: 0.93–0.94, p < 0.001).

Incidences of ACS and stroke presented with only marginal, non-significant changes during 2020/2021 (IRR: 0.98, 95% CI: 0.83–1.16, p = 0.810, IRR: 0.96, 95% CI: 0.81–1.14, p = 0.636, respectively). Incidences of both diagnoses only transiently dropped in March and April 2020 with fast recoveries as of May 2020. The in-hospital mortality for ACS and stroke did not significantly differ in 2020/2021 compared to 2015–2019 (4.1% vs. 3.7%, OR: 1.00, 95% CI: 0.91–1.10, p = 0.416 for ACS, 4.9% vs. 4.1%, OR: 1.00, 95% CI: 0.92–1.10, p = 0.964 for stroke). Median LOS decreased for ACS (2015–2019: 4 [IQR: 1 to 8] days; 2020/2021: 3 [IQR: 1 to 7] days, Wilcoxon test: < 0.001) and for stroke (2015–2019: 9 [IQR: 4 to 18] days; 2020/2021: 7 [IQR: 4 to 16] days, Wilcoxon test: < 0.001).

Discussion and conclusions

Our study showed a clear beneficial effect of the protective restrictions during the first two years of the Covid-19 pandemic on non-Covid-19 pneumonia and AECOPD hospitalizations. Both AECOPD and pneumonia were similarly reduced by those restrictions, which is not explained by general health-seeking behaviour as incidences for ACS and stroke remained stable. All-cause hospitalizations registered a significant decrease in the beginning of 2020 with a recovery to pre-pandemic levels towards late 2020. The disease severity, as indicated by hospital mortality, among patients hospitalised with AECOPD or with pneumonia was higher than in previous years.

Our observation of reduced hospitalizations with AECOPD and pneumonia can be attributed to various causes. The instruction to wear a mask, social distancing and other measures had an impact on the behaviour of the patients. We hypothesize that Covid-19 directed measures also led to fewer cases of AECOPD and pneumonia. Various studies conducted in different countries showed the same result. For example, a study in Taiwan showed a significant reduction in community-acquired pneumonias during the pandemic, which was partly attributed to Covid-19 measures that prevented droplet and faecal-oral respiratory infections in particular [13]. An observational study in Denmark attributed the reduction in severe AECOPD cases observed in 2020 partly to social distancing [14]. It is also evident that the rates of AECOPD and pneumonia are showing a gradual and steady resurgence after the previously mentioned decline. This resurgence may be linked to the progressive easing of restrictions.

In contrast, cardiovascular risk factors and thus risk factors for the non-communicable diseases ACS and stroke, such as arterial hypertension, hyperlipidaemia and obesity did not seem to be directly affected by masks and other restrictions. Accordingly, hospitalizations for ACS and stroke were only briefly reduced during the early lock-down. This indicates that healthcare utilization was initially impacted although reduction of stress-related cardiovascular events during lock-down cannot be entirely excluded. Another possibly contributing factor was a greater propensity for home care for patients with AECOPD and pneumonia during the pandemic compared to patients with ACS or stroke.

Mortality and thus severity of AECOPD and of pneumonia were slightly increased in 2020/2021. The minimal increase in pneumonia mortality (0.1%) was statistically significant, but probably of little clinical significance. Hypotheses include again delayed healthcare utilization when people were more reluctant to present themselves at the hospital out of fear of healthcare-associated Covid-19 [15]. Another reason could be the limited resources and shortage of hospital beds of overwhelmed health systems, which were focused on coping with the pandemic. This possibly led to neglect of the treatment and prevention of other diseases [16]. However, as evident from stable incidences of ACS and stroke hospitalizations, this was likely not a major effect in Switzerland except for the very beginning of the pandemic.

Interestingly, both hospitalizations for pneumonia and AECOPD decreased around the same time and to very similar proportions during 2020/2021. This suggests that the proportions which were prevented through pandemic-related restrictions are similar for both diseases which points to largely overlapping causes of AECOPD and pneumonia. This illustrates a close epidemiologic connection between these diseases, i.e. that both are primarily caused by respiratory pathogens, both viral and bacterial which are transmitted by droplets or airborne routes [17, 18]. Infectious agents can be found in up to 80% of AECOPD, but these data are affected by limited sensitivity of microbiological methods [19]. Therefore it has been suggested that infectious aetiologies are likely underestimated [20]. Our study supports this hypothesis, at least for those exacerbations which are severe enough to require hospitalization, since reductions were similar to those for pneumonia.

Strengths

This study used a nationwide database of all hospitalizations in Switzerland over 7 years. This allowed us to study not only a large number of hospital admissions but also a complete national representation. Furthermore, validated statistical methods were used to analyze this amount of data. Use of the Medstat data allowed a high temporospatial resolution of both Covid-19 cases and hospitalizations for AECOPD.

Limitations

Although infections are the most frequent reason for AECOPD [18], there are other causes, for example allergies and air pollution [21, 22]. Thus, AECOPD is not a subgroup of pneumonia, although a major part of AECOPD is triggered by infections. Due to the nature of the database which relies on ICD-10 coding provided by hospitals, there is insufficient data on causative pathogens. The location of the hospitals was only available at the cantonal level.

Our results show that pandemic-related measures were highly effective against hospitalizations for non-Covid-19 respiratory infections. These enabled the avoidance of the feared parallel epidemics of concomitant respiratory infections, which is good news for healthcare systems and individual patients alike and inform future pandemic planning. However, the possibly increased correlates of severity of hospitalized respiratory infections are concerning and require further analyses. Our data also suggest that most common causes of AECOPD are infectious as are the causes of pneumonia. These epidemiologic results thus complement imperfect diagnostic methods to delineate the aetiologies of AECOPD but should be confirmed using sophisticated microbiological methods.