Differentials

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Residence in/travel to a country/area or territory with local transmission, or close contact with a confirmed or probable case of COVID-19, in the 14 days prior to symptom onset. 

Signs and symptoms are similar so it may be difficult to differentiate between the conditions clinically.

The situation is evolving rapidly; see our COVID-19 topic for further information.

INVESTIGATIONS

Real-time reverse transcription polymerase chain reaction (RT-PCR): positive for SARS-CoV-2 RNA.

It is not possible to differentiate COVID-19 from other causes of pneumonia on chest imaging.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs/symptoms.

INVESTIGATIONS

Diagnostic studies should be considered based on local guidance as well as microbial patterns in a particular community.

Isolation of organisms such as Streptococcus pneumoniae and Staphylococcus aureus from sputum and blood culture, and through response to typical therapy.

CXR findings for typical pneumonia are consistent with consolidation.

Positive Asian lineage A(H7N9) virus-specific tests do not exclude the possibility of coinfections or bacterial super-infections. Bacterial coinfections have not been detected in most Asian lineage A(H7N9) cases; when they have occurred, bacterial species associated with hospital-associated infections and ventilator-associated pneumonia accounted for the majority of bacterial coinfections. Methicillin-resistant S aureus (MRSA) coinfection has been reported. Coinfection with bacteria associated with community-acquired pneumonia is more common in patients with seasonal influenza.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs/symptoms.

INVESTIGATIONS

Confirmation of infection by atypical pathogens (including atypical pneumonia pathogens such as Mycoplasma pneumoniae, Legionella pneumophila, and Chlamydophila pneumoniae) by sputum culture, blood culture, or other specific tests.

A diagnosis of atypical pneumonia does not rule out Asian lineage A(H7N9) virus infection, but coinfection with Asian lineage A(H7N9) virus and atypical pneumonia pathogens has not been reported.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs/symptoms.

Respiratory infections due to pathogens endemic to the region where infection occurred should be considered (e.g., endemic mycotic infection, melioidosis in parts of Southeast Asia).

INVESTIGATIONS

Diagnostic tests confirming infection caused by an atypical pneumonia organism do not rule out Asian lineage A(H7N9) virus infection, but coinfection with Asian lineage A(H7N9) virus and endemic respiratory infections has not been reported.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

More common cause of severe morbidity in young children, older adults, and people with underlying chronic medical conditions (e.g., cardiopulmonary disease, immunosuppressed). More likely to be a self-limited condition with milder symptoms among previously healthy people.

No differentiating signs/symptoms, but severe lower respiratory tract disease can also occur among previously healthy children, young adults, pregnant women, and morbidly obese people.

Seasonal influenza and Asian lineage A(H7N9) virus infection can have rapid onset of fever, cough, and pneumonia.

INVESTIGATIONS

Confirmation by diagnostic testing of infection by another respiratory virus does not rule out Asian lineage A(H7N9) virus infection. Coinfections with Asian lineage A(H7N9) and seasonal A(H3N2) and seasonal A(H1N1)pdm09 viruses have been reported.[14][133][134] A nosocomial cluster induced by coinfections with avian influenza A(H7N9) and A(H1N1)pdm09 viruses occurred in two patients at a hospital in China.[14] The implications of such influenza virus coinfections on clinical outcomes are not clear. Because there is potential for virus reassortment, detection of other influenza A virus subtypes as part of an influenza surveillance program is recommended. Rapid influenza diagnostic tests (antigen tests) lack sensitivity to detect influenza viruses and cannot distinguish between Asian lineage A(H7N9) A virus and other influenza A viruses, and should not be used to diagnose Asian lineage A(H7N9) virus infection. Commercially available influenza molecular assays have high sensitivity to detect influenza viruses in respiratory specimens, but cannot specifically identify A(H7N9) virus, or distinguish A(H7N9) virus from seasonal influenza A viruses.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Most common cause of lower respiratory tract infection in children aged <1 year.

Significant and often unrecognized cause of lower respiratory tract infection in both older and immunosuppressed patients.

Gives rise to upper and lower respiratory symptoms that peak in 3 to 5 days and resolve within 7 to 10 days.

INVESTIGATIONS

Rapid assays using antigen-capture technology are the mainstay of the diagnostic algorithm, as the identification by culture can take from 4 days to 2 weeks.[135] Molecular detection methods (polymerase chain reaction) are used increasingly to detect RSV.

Confirmation by diagnostic testing of infection by another respiratory virus does not rule out Asian lineage A(H7N9) virus infection, but coinfection with Asian lineage A(H7N9) virus and other respiratory viruses has not been reported. However, coinfections with other respiratory viruses have been identified in patients infected with A(H1N1)pdm09 and seasonal influenza viruses.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs/symptoms.

Common Middle East respiratory syndrome coronavirus (MERS-CoV) symptoms are acute, serious respiratory illness with fever, cough, shortness of breath, and breathing difficulties. Most patients had pneumonia, respiratory failure, and acute respiratory distress syndrome. Many also had gastrointestinal symptoms (including diarrhea) while others had kidney failure. Approximately more than one third of people identified with MERS-CoV to date have died.

INVESTIGATIONS

Laboratory tests (reverse transcriptase polymerase chain reaction) for MERS-CoV are not commonly available, but can be found at some international public health laboratories, particularly in regions affected by MERS-CoV infections.

Between 2012 and 30 June 2019, 27 countries (Kingdom of Saudi Arabia, Jordan, Bahrain, Egypt, Iran, Kuwait, Lebanon, Oman, Qatar, the United Arab Emirates, Yemen, Algeria, Tunisia, Austria, France, Germany, Greece, Italy, the Netherlands, Turkey, the UK, China, the Republic of Korea, Malaysia, Philippines, Thailand, and the US) have reported 2449 laboratory-confirmed cases of human infection with MERS-CoV; more than one third have died. The majority of infections were acquired in the Middle East and 84% of cases were reported by the Kingdom of Saudi Arabia. Secondary-transmission cases are common and have also been reported by countries outside of the Middle East, including 185 cases that occurred in the Republic of Korea, following a single imported case.

Nosocomial transmission is well recognized. The majority of infected healthcare workers (approximately 18% of all cases) have had mild or asymptomatic infection, but some fatal outcomes have been reported. Camels are the suspected primary source of zoonotic transmission to humans, but investigations are ongoing. When human-to-human transmission has occurred it has not been sustained.[136][137][138][139]

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