Corresponding author:
Naoyuki Miyashita, MD, PhD,
First Department of Internal Medicine,
Division of Respiratory Medicine, Infectious Disease and Allergology,
Kansai Medical University,
2-3-1 Shin-machi, Hirakata, Osaka 573-1191, Japan.
Telephone: +81-72-804-0101; Fax: +81-72-804-2504
Email:miyashin@hirakata.kmu.ac.jp
Keywords: activity of daily living, functional outcome, Omicron variant, SARS-CoV-2, COVID-19
Dear Editor
In a previous study, we demonstrated that advanced age was a risk factor for functional decline at 1 year in hospitalized elderly patients with pneumonia due to SARS-CoV-2 ancestral strain and Alpha variant [1]. The Delta variant of SARS-CoV-2 is being replaced by the Omicron variant. In a hamster model, the Omicron variant showed decreased lung infectivity and lower pathogenicity than Delta and ancestral SARS-CoV-2 [2]. Global case fatalities ranged from 1.7 to 39.0% in February to March of 2020 when the ancestral variant was predominant; however, they fell to below 0.3% in July to August 2022 when Omicron was predominant in Japan [3]. In this period, the pattern of pneumonia changed from primarily viral pneumonia to pneumonia mixed with bacteria, including aspiration pneumonia. Bacterial co-infection and secondary bacterial infection in patients with COVID-19 was low until the Delta variant [4-6].
The Japan Respiratory Society (JRS) pneumonia guidelines emphasize the importance of pneumonia prevention rather than antibiotic therapy to avoid deterioration of physical function in the elderly [7]. Functional decline after hospitalization due to pneumonia often induces aspiration pneumonia especially in those aged ≥ 80 years old after acute febrile illness such as a viral infection [7]. The objective of this study was to clarify the functional outcomes at 1 year after hospital discharge in elderly patients (≥ 80 years old) hospitalized for pneumonia due to SARS-CoV-2 Omicron variant. We compared the functional outcomes between primary viral pneumonia and pneumonia mixed with bacteria groups.
The present study was conducted at five institutions between December 2021 and August 2022. Activities of daily living (ADL) was used to calculate the Barthel Index, which consisted of the following 10 indices: feeding; bathing; grooming; dressing; bowels; bladder; toilet use; transfers; morbidity; and stairs [8]. In the present study, we calculated the difference in ADL scores between baseline (1 week before admission), at hospital discharge, and 1 year after discharge from our hospitals. The difference was categorized into two groups: declined (≥ 1) and not declined (0). Of the pneumonia cases, we excluded bedridden cases because these patients were not able to change their ADL score between before and after admission to hospital.
During the study period, 891 elderly patients with pneumonia due to SARS-CoV-2 Omicron variant were recognized. Of these, we enrolled 303 patients with primary viral pneumonia and 326 patients with pneumonia mixed with bacteria that we could follow-up for 1 year. Bacterial co-infection and secondary bacterial pneumonia were defined using bacteria detected by sputum culture or urinary antigen tests, and bacterial pneumonia prediction score using the JRS pneumonia guidelines (0 or 1 point) [9].
Functional decline rates at the time of hospital discharge were higher in the primary viral pneumonia group than the pneumonia mixed with bacteria group (52.3% vs. 40.3%, p = 0.0024) (Table 1). Of 171 patients in the pneumonia mixed with bacteria group who had a decline in physical function at the time of hospital discharge, 139 patients (81.3%) still showed functional decline at 1 year later. On the other hand, in the primary viral pneumonia group, 20.5% of patients had functional decline at 1 year after hospital discharge, which is significantly lower (p < 0.0001). Among the BA.1, BA.2, and BA.5 Omicron subvariant groups, functional decline rates at the time of hospital discharge and at 1 year after hospital discharge were similar in both groups.
In our previous study, we followed up ≥ 80 years old elderly patients with pneumonia due to SARS-CoV-2 ancestral strain and Alpha variant and demonstrated that 42.5% showed a decline in function 1 year after hospital discharge compared to their baseline ADL function [1]. In the present study, functional decline rates at 1 year after hospital discharge were significantly lower in the primary Omicron variant pneumonia group (20.5%) than the primary ancestral strain and Alpha variant pneumonia group (p < 0.0001). In contrast, functional decline rates at 1 year after hospital discharge were similar between the groups (p > 0.9999).
With the decrease in pathogenicity of Omicron variant, functional decline rates at 1 year after hospital discharge were significantly decreased in the primary Omicron variant pneumonia group compared to primary ancestral strain and Alpha variant pneumonia group. On the other hand, a high incidence of functional decline was observed in elderly Omicron pneumonia with bacterial co-infection.
Our findings suggest that physicians should recommend the use of anti-SARS-CoV-2 drugs and SARS-CoV-2 vaccination when COVID-19 is found in patients who are ≥ 80 years old even though the predominant strain is the Omicron variant.