Differentials
Coronavirus disease 2019 (COVID-19)
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 viral RNA.
It is not possible to differentiate COVID-19 from other causes of pneumonia on chest imaging.
Middle East respiratory syndrome (MERS)
SIGNS / SYMPTOMS
Caused by MERS coronavirus (MERS-CoV).
Associated with history of travel in countries of the Arabian Peninsula.
Clinical features are similar to those of SARS, but progresses to respiratory failure much more rapidly than SARS.
Primarily affects older individuals, with a male predominance.
In contrast to SARS, about 75% of patients with MERS-CoV have at least one comorbid illness.[42]
INVESTIGATIONS
Nasopharyngeal swabs (RT-PCR): positive for MERS-CoV.
Community-acquired pneumonia
SIGNS / SYMPTOMS
Lack of recent travel history to an affected area or of recent close contact with a person confirmed with or suspected of having SARS.
INVESTIGATIONS
Sputum and blood cultures: may be positive for Streptococcus pneumoniae or other bacterial pathogens.
FBC: leukocytosis and/or elevated neutrophil count. Clinical and radiological improvement with proper antibiotic therapy.
Viral respiratory infections
SIGNS / SYMPTOMS
Lack of history of recent travel to an affected area or of recent close contact with a person confirmed with or suspected of having SARS.
Unlikely to cause serious illness in young patients with no comorbidities. Upper respiratory symptoms are usually present.
INVESTIGATIONS
Nasopharyngeal virus culture and direct fluorescent antibody/ELISA: may be positive for such pathogens as influenza viruses (A and B), respiratory syncytial virus, parainfluenza viruses, and adenovirus.
Serology: useful for retrospective diagnosis.
Atypical pneumonia
SIGNS / SYMPTOMS
Lack of history of recent travel to an affected area or of recent close contact with a person confirmed with or suspected of having SARS.
Mild respiratory illness, often occurring in young people following exposure in close community settings.
INVESTIGATIONS
Serology, PCR, or culture of nasopharyngeal swabs for Chlamydia pneumoniae and Mycoplasma pneumoniae.
Sputum culture or direct fluorescent antigen detection for Legionella pneumophila.
Rapid urinary Legionella antigen detection.
Avian influenza infection
SIGNS / SYMPTOMS
Difficult to distinguish from SARS based on symptomatology as both cause a febrile lower respiratory tract illness. Historical risk factors may prove useful as avian influenza is more commonly associated with travel to a country affected with avian influenza A (H5N1) virus or direct contact with poultry or birds that may be carriers of H5N1.
INVESTIGATIONS
Pharyngeal swab: positive RT-PCR for H5-specific RNA.
Immunofluorescence antigen test: positive for antigen of H5N1 virus.
Viral culture: growth of H5N1.
Serological testing: positive for H5N1-specific antibody.
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