With the expanding use of molecular assays, viral pathogens are increasingly detected among critically ill adult patients with respiratory illness; studies have reported a prevalence between 17% and 53% of patients (Table 1), depending on study design, sample type, duration of illness, and assay methods. Common viruses that can cause severe respiratory viral infections (RVIs) include influenza A and B viruses, picornaviruses (rhinovirus, enterovirus [e.g., enterovirus D68]), human coronaviruses (229E, NL63, OC43, HKU1), respiratory syncytial virus (RSV), human metapneumovirus, parainfluenza virus, and adenovirus (Tables 1 and 2). Novel pathogens including zoonotic coronaviruses like the agents causing Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS) and the 2019 novel coronavirus (2019 nCoV) are still being identified (Table 2).
Table 1 Prevalence of community-acquired respiratory viral infections (RVIs) in critically ill patients
Study Population Patients (N) Samples Country Assays Overall prevalence or RVI Influenza Picornaviruses (rhinovirus, enterovirus) Human coronaviruses (229E, NL63, OC43, HKU1) Respiratory syncytial virus Human metapneumovirus Parainfluenza virus Adenovirus
Daubin 2006 IMV for > 48 h 187 TA France Viral culture, IFA, NAAT 32 (17%) Influenza A 7 (4%) Rhinovirus 19 (10%)
Enterovirus 2 (1%) 1 (0.5%) 2 (1%) 0 (0%) 1 (0.5%) 1 (0.5%)
Cameron 2006 COPD exacerbation requiring NIV or IMV 105 PS Australia IFA, viral culture, NAAT, serology 46 (43%) Influenza A 14 (13%)
Influenza B 6 (6%) Rhinovirus 7 (7%)
Enterovirus 2 (2%) 3 (3%) 7 (7%) 3 (3%) 11 (10%) 0 (0%)
Schnell 2014 Acute respiratory failure 70, 47 (67%) mechanically ventilated PS, BAL France IFA, NAAT 34 (49%) Influenza A 11 (16%)
Influenza B 2 (3%) Rhinovirus 6 (9%) 5 (7%) 4 (6%) 4 (6%) 1 (1%) 3 (4%)
Legoff 2005 Acute pneumonia admitted to ICU 41 BAL France Viral culture, IFA, NAAT 13 (32%) Influenza A 7 (17%)
Influenza B 1 (2%) 0 (0%) 0 (0%) 2 (5%) 0 (0%) 2 (5%) 2 (5%)
Wiemken 2013 Severe CAP admitted to ICU 468, 84% adults PS USA NAAT 106 (23%) Influenza 38 (8%) Rhinovirus 40 (9%) 0 (0%0 8 (2%) 15 (3%) 4 (1%) 1 (0.2%)
Karhu 2014 Severe CAP 49 PS, BAL, TA Finland NAAT 24 (49%) 1 (2%) Rhinovirus 15 (30%)
Enterovirus 2 (4%) 2 (4%) 1 (2%) 0 (0%) 1 (2%) 4 (8%)
Tramuto 2016 ILI admitted to ICU 233 PS, BAL Italy NAAT 102 (44%) 57 (24%) Rhinovirus 7 (3%)
Enterovirus 14 (6%) 11 (5%) 8 (3%) 16 (7%) 16 (7%) 0 (0%)
Choi 2019a Severe CAP admitted to ICU 1559 PS, BAL Republic of Korea NAAT Not reported 109 (7.0%) Rhinovirus 120 (8%) 56 (4%) 52 (3%) 50 (3%) 71 (5%) Not reported
Shorr 2018 Severe CAP and HCAP requiring IMV 364 sputum, TA, BAL USA NAAT 65 (18%) Influenza A 12 (3%)
Influenza B 1 (0.3%) Rhinovirus/Enterovirus 20 (5%) Not reported 11 (3%) 8 (2%) 7 (2%) 6 (2%)
Legoff 2018 Hematology patients admitted to ICU 747 PS France NAAT 163 (22%) 20 (3%) 92 (12%) 22 (3%) 18 (2%) 4 (0.5%), 12 (2%) 5 (0.6%)
Voiriot 2016 Severe CAP admitted to ICU 174 PS, TA, BAL France NAAT 93 (53%) Influenza A 32 (18%) Influenza B 6 (3%) Rhinovirus/Enterovirus 22 (13%) 14 (8%) 9 (5%) 12 (7%) 3 (2%) 3 (2%)
Arabi 2018 Severe acute respiratory infection admitted to ICU 222 PS, TA, BAL Saudi Arabia NAAT 43 (19%) Influenza A 29 (13%) Influenza B 3 (1%) Rhinovirus 9 (4%)
Enterovirus 0 (0%) 5 (2%) 1 (0.5%) 1 (0.5%) 1 (0.5%) 1 (0.5%)
Overall prevalence is reported here for influenza, picornaviruses (rhinovirus, enterovirus), human coronaviruses (229E, NL63, OC43, HKU1), respiratory syncytial virus, human metapneumovirus, parainfluenza virus, and adenovirus. Please refer to the online supplement for references. Studies varied in the approach for sampling and in the used assays; in some studies, specimen collection and assays were standardized across all patients, while in other studies, sampling and assays were performed selectively. All percentages represent % of patients; some patients had more than one viral pathogen isolated
IMV invasive mechanical ventilation, TA tracheal aspirate, IFA immunofluorescence assay, NAAT (nucleic acid amplification test) includes commercial and in-house PCR, RT-PCR, and PCR multiplex, COPD chronic obstructive pulmonary disease, NIV non-invasive ventilation, PS nasopharyngeal specimen including nasopharyngeal or oropharyngeal aspirates or swabs, BAL bronchoalveolar lavage, CAP community-acquired pneumonia, ILI influenza-like illness, HCAP healthcare-associated pneumonia
aMultiple publications exist from the same cohort. We included the most recent one (Supplementary references)
Table 2 Common and uncommon community-acquired respiratory viruses that may cause severe respiratory viral infection
Virus Epidemiologic and clinical features Additional infection control precautionsa
Common respiratory viruses
Influenza A and influenza B Only influenza type A viruses are known to have caused pandemics
Currently circulating seasonal influenza A viruses in humans: subtype A(H1N1)pdm09 and A(H3N2) strains
Currently circulating influenza B viruses: A/Victoria-like, A/Yamagata-like strains
May be associated with acute myocardial infarction, myocarditis, rhabdomyolysis, acute renal failure, encephalopathy/encephalitis, and other non-pulmonary complications Droplet
Picornaviruses (rhinovirus, enterovirus) Frequently detected in critically ill patients with severe acute respiratory infection.
May cause severe illness in the elderly, persons with co-morbidities including immunosuppression. Droplet
Human coronaviruses (229E, NL63, OC43, HKU1) Contact
Respiratory syncytial virus Contact
Human metapneumovirus Contact
Parainfluenza (1-4) Contact
Adenoviruses Droplet + contact
Uncommon and emerging viruses
Avian influenza A/H5N1, A/H5N6, A/H7N9 and other subtypes Residence in or travel to Southeast and East Asia
Exposure to poultry or visit to poultry market Airborne + contact
MERS-CoV Residence in or travel to the Arabian Peninsula
Exposure to dromedary camel (in endemic areas)
Nosocomial transmission risk to other patients and to healthcare workers Airborne + contact
SARS-CoV No cases have been reported since 2004
Nosocomial transmission risk to other patients and to healthcare workers Airborne + contact
2019 Novel coronavirus (2019 nCoV) As of February 4, 2020, 20630 cases were reported from China and 23 other countries Droplet + contact and wherever possible airborneb
Measlesc Incomplete vaccination
Characteristic rash. Progressive giant cell pneumonia without rash may occur in immunocompromised (Hecht’s pneumonia) Airborne
Hantaviruses (e.g., Sin Nombre, Andes)c Residence in or travel to affected areas of North, Central, or South America
Exposure to rodent excretions particularly when cleaning buildings Standard
Varicella-zoster virusc Incomplete vaccination, pregnancy
Often with characteristic rash Airborne + contact
Please refer to the online supplement for references
Infection control precautions are based on the Centers for Disease Control and Prevention at: https://www.cdc.gov/infectioncontrol/guidelines/isolation/appendix/type-duration-precautions.html#M, https://www.cdc.gov/coronavirus/mers/infection-prevention-control.html, https://www.cdc.gov/infectioncontrol/guidelines/isolation/appendix/standard-precautions.html, https://www.cdc.gov/flu/professionals/infectioncontrol/healthcaresettings.htm (all accessed on Dec 10-2019)
aAll suspected or confirmed RVIs require minimum of standard precautions. Eye protection is a reasonable addition to droplet isolation as the ocular route of infection has been documented for several common respiratory viruses
bData on the novel coronavirus are based on the WHO interim report as of February 4, 2020
cOther viral pathogens with respiratory routes of acquisition