Discussion
Our study characterised the incidence proportions for Omicron-associated pneumonia, as well as the prognosis of inpatients with pneumonia, and also analysed the laboratory indices to evaluate the relationship with disease severity. All of the study patients were infected with the Omicron variant and received care at our hospital.
Age, gender, lung cancer, BDCSs and kidney disease all had a significant difference of incidence proportion on the incidence of pneumonia; age had the most apparent difference. As people age, immunity gradually wanes, thus older patients had a higher risk of pneumonia. COVID-19 as a respiratory system disease often causes respiratory symptoms and it is generally believed that patients with BDRSs will have more severe symptoms; however, we characterised that patients with BDRSs did not have the higher incidence proportion of pneumonia. In fact, patients with lung cancer had a lower odd of incidence of pneumonia. Influenza virus infection is also a type of respiratory system disease that can cause pneumonia. Several studies have reported the risk factors for influenza virus-associated pneumonia, all of which demonstrated BDRSs to be a risk factor.8–10 This outcome was in inconformity to the lower incidence proportion of Omicron-associated pneumonia in patients with lung cancer. Based on our study results, patients with BDCSs or kidney disease had a higher incidence proportion of pneumonia. Although COVID-19 is a respiratory infectious disease, we suggest that the main cause of pneumonia caused by Omicron is not a respiratory infection, but to circulatory system-related or kidney-related factors. The specific pathogenesis underlying Omicron variant infection-associated pneumonia warrants further study.
The prognosis for patients with Omicron variant infection-associated pneumonia depends on the severity of the disease, thus we divided patients into two groups to analyse the impact of each factor more accurately. Patients in the ROI group with BDRSs did not have a lengthy hospital stay and usually had a favourable prognosis. In contrast, patients in the NIV and MV group with BDRSs were at an increased risk of death, perhaps because BDRSs increase the risk of ARDS. Thrombosis is one of the complications of COVID-19 infection, and usually causes severe clinical symptoms.11–13 According to the guidelines, we administered prophylactic anticoagulation therapy to patients without contraindications. For patients with contraindications or who failed prevention, thrombosis was still an important factor affecting prognosis. Steroid, as a type of anti-inflammatory drug, can effectively promote the absorption of pneumonia.14 In clinical practice, we often prescribed the dose of steroid according to the severity (determined by patients’ symptoms, imaging manifestations and blood gas indexes). We collected steroid programmes from every inpatient and performed the subgroups analysis (online supplemental figure 2–4). The outcomes showed higher dose of steroid was used in more severe patients. In the ROI group, versus without steroid therapy, the longer hospitalisation time in patients who prescribed steroid therapy may be due to the higher dose of steroid and its duration of treatment. Online supplemental figure 4) showed there is no best daily dose of steroid to reduce hospitalisation time and mortality. Therefore, we should adjust the dose of steroid according to the state of illness in time. Paxlovid as a new antiviral drug came into use in our hospital in December 2022. The effect of this drug was not evident in ROI patients, but paxlovid significantly reduced the risk of death in NIV or MV patients. Immunoglobulins are not recommended according to the guidelines, but our findings showed that immunoglobulins significantly reduced the risk of death in NIV or MV patients. Based on these outcomes, the efficacy of paxlovid and immunoglobulins in NIV and MV patients require further study.
The changes in the following laboratory indices were more apparent in the NIV and MV group than the ROI group: the number of neutrophils and lymphocytes and myoglobin, LDH, AST and PCT levels and PO2. We believe these indices can be used to classify disease severity in patients infected with the Omicron variant. Neutrophils, lymphocytes and PCT are markers of infection, and an inflammatory response increases in which correlate with severity in pneumonia patients. Thus, the more severe infection, the stronger the inflammatory response. The PO2 was lower in the NIV and MV patients than the ROI patients, which explains, at least in part, why patients with severe pneumonia progress to ARDS. The myoglobin, LDH and AST levels, which are markers of acute myocardial or liver injury, were higher in NIV and MV patients. These findings explained why patients with severe pneumonia also had severe myocardial and liver injuries. Previous studies have reported similar outcomes,15–19 but currently there are no established laboratory indices for determining the severity of COVID-19. We hope these findings provide guidance and a larger cohort study can be conducted to determine the clinical usefulness of these indices.
Our study analysed the incidence proportions for pneumonia caused by Omicron infection, then determined the prognosis of hospitalised patients with pneumonia and finally compared the laboratory indices among patients with different levels of pneumonia severity. This was the first study to report the pathogenic characteristics of Omicron in Chinese patients since COVID-19 became prevalent in China in December 2022. In addition, to our knowledge, this is the first study to discuss the incidence proportion of Omicron-associated pneumonia in patients with different basic diseases. Further studies should be held to discuss the underlying relationship between Omicron-associated pneumonia and basic disease, which can help us to protect the susceptible population and also help us to research the specific pathogenesis underlying Omicron variant infection-associated pneumonia.
There were limitations in our study. Because of the limited number of patients, we could not classify the basic diseases more accurately. For example, with respect to the prognosis analysis, there were few cases in each type of BDRSs; specifically, only four hospitalised patients had lung cancer and two patients had interstitial lung disease, thus we created an ‘others’ category. The same issue arose for BDCSs and other coexisting diseases. In addition, for the same reason, we combined patients who received NIV and MV into the same group. According to guidelines, such patients had different levels of disease severity, but the symptoms were more serious than the patients in the ROI group. Further studies should be conducted to discuss the influence of these prognostic factors and laboratory indices in better defined groups.
Since December 2022, Omicron has caused a widespread pandemic in China. Individuals had different clinical symptoms and the prognosis is usually different. Pneumonia, especially severe pneumonia, mainly occurs in the elderly, which has a significant impact on survival. Thus, it is especially important to accurately identify the high-risk factors for pneumonia to protect the susceptible population. For patients who have been infected with the Omicron variant and have pneumonia, dividing the severity in time to formulate appropriate treatment programmes can result in a good prognosis for most patients. The treatment of COVID-19 warrants additional studies. Paxlovid, as a new type of antiviral drug, clearly improves the prognosis of severe pneumonia patients, but the high price may be an economic burden for many families. Optimising the diagnosis and treatment procedure of COVID-19 and formulating complete treatment programmes are very important.