In-Hospital Outcomes of Healthcare-Associated COVID-19 vs Influenza

Distinguishing healthcare-associated COVID-19 from healthcare-associated influenza is important since both pathogens today continue to cause severe disease in hospitalized patients. Knowing whether the in-hospital outcomes for these two pathogens differ will assist in the management of individual patients as well as health system planning. In a large retrospective nationwide cohort study conducted in Switzerland, 30-day in-hospital mortality and ICU admission rates for healthcare-associated COVID-19 in the Omicron era were similar to those for healthcare-associated influenza, differing from earlier pandemic observations and supporting a unified approach to the management of hospital-acquired respiratory pathogens.

Why It Matters

Outcomes of healthcare-associated cases of COVID-19 and seasonal influenza can provide insights for infection control strategies, monitoring priorities, and resource allocation. While severe healthcare-associated COVID-19 has been characterized by prolonged ICU stay and high need for extraordinary surge capacity for much of the pandemic, a shift in the dynamics of severe disease is underway. Severe disease risk for COVID-19 may be decreasing; evidence supports the use of antiviral treatments to decrease transmission of severe acute respiratory syndrome coronavirus 2 safely; and recent viral variants are expected to alter the severity of COVID-19. We review current national and international data to inform public health and hospital-based planning regarding in-hospital risk of COVID-19 relative to seasonal influenza. The data suggest that there is a trend toward more similar severe outcomes in recent waves of COVID-19 and in seasonal influenza, warranting hospital planning for triage, staffing, and adequate ICU readiness.

The similarity of these prognostic indicators for the risk of ICU admission, need for mechanical ventilation, and death due to healthcare-associated COVID-19 and influenza has important implications for the design of early warning systems and escalation criteria for healthcare facility-based triage and allocation of critical care resources. However, while the risk of ICU admission and death due to healthcare-associated COVID-19 and influenza may be similar, differences in the use of antiviral therapies and other adjunctive treatments for patients with suspected or confirmed influenza versus COVID-19 suggest that early warning systems and clinical escalation criteria for suspected influenza may differ from those for COVID-19. Prognostic indicators identified in studies of patients with COVID-19 from the early pandemic should not be assumed to apply in all settings and time periods. Rather, local epidemiology and SARS-CoV-2 variants of concern/interest will continue to play a critical role in predicting the need for critical care resources, as well as counseling patients and families on the likelihood of severe illness during respiratory season to prevent under- and overtriage.

Findings from this study can be applied to infection prevention and control policies and public health messaging for vaccination, testing, and isolation of persons with co-infection with SARS-CoV-2 and influenza. Future public health messaging and vaccination campaigns could differentiate between the two pathogens with respect to severity of disease. Messages and policies regarding the risk of transmission and the need for testing of patients and healthcare workers could also be adapted to reflect the differing risks of transmission and severity of illness for these two pathogens. Hospital-based surveillance of healthcare-associated respiratory infections could be modified to reflect these differences. Testing strategies and patient isolation precautions could be standardized for similar levels of risk, while allowing for pathogen-specific precautions for persons at greater risk of severe illness.

Who it affects

Evidence regarding healthcare outcomes must be translated to practice (at the bedside) and to policy (at the hospital). Those most able to translate the evidence to practice and policy are the clinicians from the acute care hospital setting, including a variety of specialists involved in infection control including the acute care hospitalist, emergency physician, critical care intensivist, and infection preventionist. This proof-of-concept study aims to identify evidence that can inform triage and monitoring of patients with healthcare-associated COVID-19 and with healthcare-associated influenza. For example, knowing that the percentage of patients admitted with healthcare-associated influenza who were admitted to the ICU was similar to that in one large national cohort of patients with healthcare-associated COVID-19 could help inform triage thresholds and strategies for frequency of monitoring that are similar for both pathogens with pathogen-specific therapy indicated when appropriate.

Patients with certain medical conditions (e.g. cardiovascular disease, diabetes, chronic lung disease, obesity) are more likely to have poorer outcomes due to their underlying illness. As a result, older patients and those with chronic diseases are at particularly increased risk for severe complications from COVID-19. All patients with healthcare-associated respiratory infection should have a high index of suspicion for COVID-19 or influenza, particularly the vulnerable inpatients, and promptly undergo diagnostic evaluation and targeted therapy (including antiviral therapy when appropriate). Several case reports and a series of three such cases illustrate how early recognition of illness and timely treatment can alter the clinical course for vulnerable patients.

In addition to the clinical implications for individual patients with COVID-19, those for hospital administrators and for broader policymaking come under scrutiny. Available data suggest that for the cases diagnosed to date, COVID-19 and influenza have similar in-hospital mortality rates and ICU admission rates. As a result, using combined respiratory-season scenarios when projecting surge needs can facilitate a more efficient allocation of hospital beds, oxygen, personnel, and antiviral medications for these patients. Vaccinating against both COVID-19 and influenza will remain an important strategy to prevent severe illness in vulnerable patients. The World Health Organization and CDC will continue to monitor available evidence to inform national prevention strategies.

Family members and caregivers of patients with Acute Illness may also be affected by the illness. It is important that patients, families and caregivers have an accurate understanding of what to expect in terms of the outcomes of illness and hospitalization, the expected progression of illness over time (including periods of worsening or improvement), and the likelihood of needing Intensive Care Unit (ICU) level care. Additionally, an understanding of the risks and benefits is important in making informed decisions about treatment, such as the use of medications with potential for harm (such as some antiviral medications) and other intense medical treatments with the potential for transfer to the ICU. Finally, shared decision making with patients and families regarding prognostic expectations is important.

What changes

• Hospitals can update clinical pathways to treat healthcare-associated respiratory infections more uniformly while preserving necessary pathogen-specific steps. A practical pathway begins with early detection, timely testing to identify the agent, assessment of severity and comorbidities, appropriate use of antivirals or supportive therapy, and application of infection control measures to limit spread. Where recent evidence shows comparable in-hospital mortality and similar low ICU admission rates for healthcare-associated COVID-19 and influenza, many institutions can streamline early monitoring triggers and bedside escalation criteria, then layer on disease-specific therapies such as neuraminidase inhibitors for influenza or oral antivirals for COVID-19 when indicated.
• Resource allocation can be informed by the observed rates of severe outcomes. For example, the Swiss cohort reported that about 2 to 3 percent of hospitalized healthcare-associated cases required ICU support for either pathogen, which suggests that ICU surge models for combined respiratory seasons should account for these proportions when estimating bed and staff needs. Administrators should also consider indirect burdens such as isolation needs, additional nursing time, and post-discharge follow-up. Planning for antiviral availability, oxygen systems, and rehabilitation services remains essential, regardless of whether COVID-19 or influenza predominates.
• Preventive and public health measures remain key and should be reinforced. Vaccination campaigns, early detection strategies, staff vaccination and sick-leave policies, and targeted testing in high-risk wards help reduce healthcare-associated transmission. In facilities with high-risk patient populations, continued emphasis on vaccination for both influenza and COVID-19, use of personal protective equipment during respiratory seasons, and rapid outbreak response protocols will reduce overall in-hospital morbidity and mortality. National and international guidance should be used to update local protocols, but clinicians must tailor policies to local incidence, dominant variants, and hospital capacity.
• Clinical practice should emphasize early, evidence-based treatment and careful patient selection for escalation. Even when aggregate mortality rates are comparable, some patient subsets will do worse with one pathogen than another. Early antiviral therapy for influenza reduces severe outcomes when started promptly in high-risk patients. For COVID-19, effective antivirals and monoclonal therapies in the appropriate window can reduce progression in high-risk individuals. Close monitoring, early supportive care including supplemental oxygen and thrombosis prevention when appropriate, and timely ICU transfer for organ support remain cornerstones of care. Clinicians should also remain aware that older data from earlier pandemic waves showed higher ICU resource needs and longer stays for COVID-19, so historical experience still informs vigilance and clinical judgment.
• Data, surveillance, and research priorities should be sustained. Ongoing surveillance of healthcare-associated infections, variant tracking, and prospective studies comparing pathogen-specific outcomes are crucial. As SARS-CoV-2 continues to evolve, continuous evaluation of in-hospital outcomes will tell us whether current parity with influenza persists, improves, or reverses. Hospitals should invest in robust electronic surveillance systems and contribute to national registries to support timely comparisons and evidence-based policy. Practical recommendations for clinicians and systems Adopt standardized detection and escalation pathways for any new respiratory symptoms developing after 48 to 72 hours of admission. Confirm the pathogen by testing, assess severity using objective measures such as oxygen saturation, respiratory rate, inflammatory markers, and imaging when indicated, and initiate appropriate therapy quickly when indicated. Early warning scores can help nursing and medical teams recognize clinical deterioration before severe hypoxia or organ dysfunction develops. Clear documentation of symptom onset, exposure history within the hospital, and timing of diagnostic testing also supports accurate classification of healthcare-associated infection. Hospitals should ensure that rapid testing platforms are readily accessible so that treatment decisions are not delayed while awaiting results. Use risk stratification to guide therapy and disposition. cOlder age, multiple comorbidities, frailty, and markers of organ dysfunction such as rising creatinine, hypotension, or increasing oxygen requirement should prompt more aggressive monitoring and lower thresholds for ICU consultation. Patients with compromised immunity, advanced cardiac or lung disease, or poorly controlled diabetes require closer observation because they may deteriorate more quickly. Structured risk assessment tools and multidisciplinary review rounds can improve consistency in escalation decisions and reduce variability in care between teams. Coordinate infection prevention measures with clinical care pathways. Isolation, PPE use, and staff cohorting reduce nosocomial spread and protect vulnerable patients. Maintain strong communication with patients and families. Discuss expected timelines, likely interventions, and the possibility of ICU care. Explain how preventive measures such as vaccination reduce the chance of serious healthcare-associated disease. Keep policies flexible and data-driven. Use local and national surveillance data to adjust testing, treatment, and isolation policies in real time. Conclusion Understanding in-hospital outcomes for healthcare-associated COVID-19 compared with influenza helps hospitals and clinicians design safer, more efficient care pathways that match current risk profiles. Recent large cohort evidence showing similar 30-day in-hospital mortality and low, comparable ICU admission rates for healthcare-associated infections caused by either pathogen supports harmonized clinical pathways while maintaining pathogen-specific treatments. However, historical and concurrent studies have shown variability across settings and time periods, so local surveillance, continued vaccination, readiness for ICU surge, and patient-centered clinical judgment remain essential. Continued research and data sharing will clarify how these risks evolve and support the safest possible care for hospitalized patients.

References:

https://www.acpjournals.org/doi/10.7326/acph-20241120-outcomes-similar-with-hospital-acquired-covid-19-vs-flu-swiss-study-finds https://www.cdc.gov/flu/whats-new/2023-2024-hospital-outcomes.html https://pmc.ncbi.nlm.nih.gov/articles/PMC12388448/