After the unusually mild 2020-2021 influenza (flu) season, which was caused in part by the community mitigation factors used to control the spread of COVID-19, it's evident that the seasonal spread of flu has returned. Flu season has started, and seasonal flu activity is elevated in many parts of the country.
Given the similarities between symptoms of influenza and COVID-19, distinguishing between the two diseases when both are spreading in the community is challenging based on symptoms alone. It's important that healthcare professionals know how to evaluate, test, and treat patients who present with symptoms consistent with either flu or COVID-19.
This is especially important for patients who are at higher risk of developing serious complications from flu, mainly because early treatment with flu antivirals can help keep high-risk patients out of the hospital, reduce the amount of time they are sick, and reduce their chance of dying of flu. Early treatment with influenza antivirals is important because it can lessen symptoms as well as reduce the risk for severe illness.
For the pandemic, testing is important to help control the spread of the virus that causes COVID-19.
CDC has developed clinical algorithms to guide clinicians in how to evaluate, test, and treat patients with influenza or COVID-19 when both are spreading in the community. These algorithms are based on local influenza activity and include information on specimen collection, testing, treatment, and infection control. These algorithms account for illness severity and healthcare setting (eg, inpatient, outpatient, long-term care facility).
When testing for SARS-CoV-2 and influenza, it is important to implement recommended infection prevention and control measures.
Guidance for Outpatient Clinic or Emergency Department Patients With Acute Respiratory Illness Symptoms (With or Without Fever) Not Requiring Hospital Admission
Specimen Collection
Collect respiratory specimens for influenza and SARS-CoV-2 testing. (Only one specimen is needed if multiplex testing for influenza and SARS-CoV-2 is available. Two different specimens may need to be collected if multiplex testing is unavailable on-site.)
SARS-CoV-2 and Influenza Virus Testing
Test for SARS-CoV-2 by nucleic acid detection or, if not available, by SARS-CoV-2 antigen detection assay.
Test for influenza if results will change clinical management or infection control decisions (eg, long-term care facility resident returning to a facility, or a person of any age returning to a congregate setting). If influenza testing is appropriate, order rapid influenza nucleic acid detection assay. If rapid influenza nucleic acid detection assay is not available on-site, order rapid influenza antigen detection assay.
Influenza Treatment
Prescribe influenza antiviral treatment if on-site influenza testing is positive or prescribe empirical influenza antiviral treatment without influenza testing based upon a clinical diagnosis of influenza for patients of any age with progressive respiratory disease of any duration, and for children and adults at higher risk for influenza complications (encourage patients to start antiviral treatment as soon as possible).
For adult patients with suspected community-acquired pneumonia who do not require hospitalization, see antibiotic treatment recommendations from the American Thoracic Society-Infectious Diseases Society of America Adult Community-acquired Pneumonia Guidelines.
Full treatment guidelines are available here.
Follow isolation recommendations for SARS-CoV-2, and arrange follow-up for any pending testing results.
Guidance for Patients With Acute Respiratory Illness Symptoms Requiring Hospital Admission (With or Without Fever)
Specimen Collection
Collect respiratory specimens for influenza and SARS-CoV-2 testing. (Only one specimen is needed if multiplex testing for influenza and SARS-CoV-2 is available. Two different specimens may need to be collected if multiplex testing is unavailable on-site.)
SARS-CoV-2 and Influenza Virus Testing
Order multiplex nucleic acid detection assay for influenza A/B/SARS-CoV-2. If not available, order SARS-CoV-2 nucleic acid detection assay and influenza nucleic acid detection assay (If a SARS-CoV-2 nucleic acid detection assay is not available on-site and a SARS-CoV-2 antigen detection assay is used, confirm negative SARS-CoV-2 antigen detection assay results by SARS-CoV-2 nucleic acid detection assay at an outside laboratory).
In critically ill intubated and mechanically ventilated patients who are suspected to have COVID-19 or influenza without a confirmed diagnosis, including when upper respiratory tract specimens are negative, lower respiratory tract (eg, endotracheal aspirate) specimens should be collected for SARS-CoV-2 and influenza virus testing by nucleic acid detection assay, per NIH COVID-19 Treatment Guidelines and Infectious Diseases Society of America Influenza Clinical Practice Guidelines.
Influenza Treatment
If bacterial pneumonia or sepsis is suspected, consider testing recommendations and empiric antibiotic treatment per American Thoracic Society-Infectious Diseases Society of America Adult Community-acquired Pneumonia Guidelines, and administer supportive care and treatment for suspected or confirmed COVID-19 patients per NIH COVID-19 Treatment Guidelines.
Start empirical oseltamivir treatment for suspected influenza as soon as possible regardless of illness duration, without waiting for influenza testing results, per Infectious Diseases Society of America Influenza Clinical Practice Guidelines, and administer supportive care.
A consolidated version of this guidance for patients requiring and not requiring hospitalization is available here.
Testing and Management Considerations for Nursing Home Residents With Acute Respiratory Illness Symptoms When SARS-CoV-2 and Influenza Viruses Are Co-circulating
There are additional practices that may be considered for nursing home residents when SARS-CoV-2 and influenza viruses are co-circulating in a community, based on local public health and healthcare facility surveillance data.
A complete list of testing and management considerations for nursing home residents with acute respiratory illness symptoms when SARS-CoV-2 and influenza viruses are co-circulating can be found here. Although these considerations are specific to care of residents residing in nursing homes, some practices could be adapted for use in other long-term care settings (eg, assisted living facilities).
Multiplex Assays
A complete list of multiplex assays authorized by FDA for simultaneous detection of influenza viruses and SARS-CoV-2 is available here.
Resources
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Public Information from the CDC and Medscape
Cite this: What Healthcare Professionals Need to Know for Testing and Treatment of Co-circulating COVID-19 and Influenza Viruses - Medscape - Jan 19, 2022.
