Background: Many adults and some children with COVID-19 or acute respiratory infection become critically ill and need advanced life support in the Intensive Care Unit (ICU). Frailty is a medical condition of reduced function and health. Adults with frailty have a lower chance of surviving critical illness. The investigators are still learning about critically ill adults with COVID-19 or acute respiratory infection, and do not have much information on how frailty affects outcomes in critically ill children, with or without COVID-19 or acute respiratory infection. Rehabilitation can help survivors of COVID-19 or acute respiratory infection by improving strength and improve quality of life (QOL).

Objectives: The main goal of this research study is to see if patients with frailty have a lower chance of surviving COVID-19 or acute respiratory infection critical illness and more health problems after survival than patients without frailty. The investigators will also study the types of rehabilitation received by patients with COVID-19 or acute respiratory infection.

Methods: The investigators will include adults and children with COVID-19 or acute respiratory infection who are admitted to the ICUs that participate in the study. The investigators will gather data about each patient, including before and during their illness.

Outcomes: The investigators will collect level of frailty, function, and types of therapy, or rehabilitation received by patients. In adults, the investigators are most interested in learning if frailty influences mortality, or death. In children, the investigators are most interested in whether children with COVID-19 or acute respiratory infection critical illness are more likely to develop frailty. The investigators will also study post-hospital discharge location in survivors (e.g., home, rehabilitation).

Relevance: The COVID-19 pandemic is a global public health crisis. It is critical to understand how COVID-19 and other acute respiratory infection critical illness affects groups of people who are at higher risk, and the impact on outcomes that are important to patients, like functioning and QOL. The results will help policy makers plan post-hospital services for survivors, help healthcare workers understand the importance of rehabilitation practice for patients with COVID-19 or acute respiratory infection, and help researchers develop treatments to improve QOL after COVID-19 or acute respiratory infection.

Inclusion Criteria:

• Adult and pediatric survivors of COVID-19 or acute respiratory infection admitted to participating intensive care units (ICUs) and PICUs. The investigators define children as less than, and adults as greater than or equal to, 18 years old, respectively. The investigators will include adults and pediatrics with a confirmed diagnosis of COVID-19, pediatric patients with MIS-C, and adults and pediatrics with suspected or proven acute respiratory infection with onset within 14 days of ICU/PICU admission and requiring invasive mechanical ventilation, non-invasive ventilation, or high flow oxygen therapy.

Exclusion Criteria:

• Patients who were admitted to ICU for <24 hours

Adult and pediatric survivors of COVID-19 or acute respiratory infection admitted to participating intensive care units (ICUs) and PICUs. The investigators define children as less than, and adults as greater than or equal to, 18 years old, respectively. The investigators will include adults and pediatrics with a confirmed diagnosis of COVID-19, pediatric patients with MIS-C, and adults and pediatrics with suspected or proven acute respiratory infection with onset within 14 days of ICU/PICU admission and requiring invasive mechanical ventilation, non-invasive ventilation, or high flow oxygen therapy.