Differentials

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Lack of residence in/travel history to an area with ongoing transmission, or lack of close contact with a suspected/confirmed case of COVID-19 in the 14 days prior to symptom onset.

Differentiating COVID-19 from community-acquired bacterial pneumonia is not usually possible from signs and symptoms. However, patients with bacterial pneumonia are more likely to have rapid development of symptoms and purulent sputum. They are less likely to have myalgia, anosmia, or pleuritic pain.[452][453]

INVESTIGATIONS

Blood or sputum culture or molecular testing: positive for causative organism.

RT-PCR: negative for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA (co-infections are possible).

CT chest: centrilobular nodules, mucoid impactions.[454]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Lack of residence in/travel history to an area with ongoing transmission, or lack of close contact with a suspected/confirmed case of COVID-19 in the 14 days prior to symptom onset.

Differentiating COVID-19 from community-acquired respiratory tract infections is not possible from signs and symptoms.

A small case-control study found that new-onset smell and/or taste disorders were more common among patients with COVID-19 compared with patients with influenza.[455]

INVESTIGATIONS

RT-PCR: positive for influenza A or B viral RNA; negative for SARS-CoV-2 viral RNA (co-infections are possible).

CT chest: there is emerging evidence that CT can be used for differentiating between influenza and COVID-19. COVID-19 patients are more likely to have rounded or linear opacities, crazy-paving sign, vascular enlargement, and interlobular septal thickening, but less likely to have nodules, tree-in-bud sign, bronchiectasis, and pleural effusion.[456][457]

Inflammatory markers and coagulation screen: there is emerging evidence that inflammatory markers (lactate dehydrogenase, erythrocyte sedimentation rate, C-reactive protein) and coagulation parameters are not as high in patients with influenza compared with COVID-19.[458]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Lack of residence in/travel history to an area with ongoing transmission, or lack of close contact with a suspected/confirmed case of COVID-19 in the 14 days prior to symptom onset.

Differentiating COVID-19 from community-acquired respiratory tract infections is not possible from signs and symptoms.

INVESTIGATIONS

RT-PCR: positive for causative organism; negative for SARS-CoV-2 viral RNA (co-infections are possible).

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Lack of residence in/travel history to an area with ongoing transmission, or lack of close contact with a suspected/confirmed case of COVID-19 in the 14 days prior to symptom onset.

Differentiating COVID-19 from community-acquired respiratory tract infections is not possible from signs and symptoms.

Adenovirus and Mycoplasma should be considered in clusters of pneumonia patients, especially in closed settings such as military camps and schools.

INVESTIGATIONS

Blood or sputum culture of molecular testing: positive for causative organism.

RT-PCR: negative for SARS-CoV-2 viral RNA (co-infections are possible).

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Lack of residence in/travel history to an area with ongoing transmission, or lack of close contact with a suspected/confirmed case of COVID-19 in the 14 days prior to symptom onset.

Differentiating COVID-19 from aspiration pneumonia is not usually possible from signs and symptoms. 

INVESTIGATIONS

RT-PCR: negative for SARS-CoV-2 viral RNA (co-infections are possible).

CT chest: difficult to distinguish on CT; however, anterior lung involvement may be more suggestive of COVID-19 pneumonia.[459]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Lack of residence in/travel history to an area with ongoing transmission, or lack of close contact with a suspected/confirmed case of COVID-19 in the 14 days prior to symptom onset.

Differentiating COVID-19 from pneumocystis jirovecii pneumonia is not usually possible from signs and symptoms.

Patients are usually immunocompromised (e.g., HIV positive) and duration of symptoms may be longer. 

INVESTIGATIONS

Sputum culture: positive for Pneumocystis.

RT-PCR: negative for SARS-CoV-2 viral RNA (co-infections are possible). 

CT chest: ground-glass opacity is usually more diffusely distributed with a tendency to spare the subpleural regions.[454]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Travel history to the Middle East or contact with a confirmed case of MERS.

Differentiating COVID-19 from MERS is not possible from signs and symptoms.

Initial data suggest that the clinical course of COVID-19 is less severe and the case fatality rate is lower compared with MERS.

INVESTIGATIONS

Reverse-transcriptase polymerase chain reaction (RT-PCR): positive for MERS-CoV viral RNA.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

There have been no cases of SARS reported since 2004.

INVESTIGATIONS

RT-PCR: positive for severe acute respiratory syndrome coronavirus (SARS-CoV) viral RNA.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

May be difficult to differentiate based on epidemiological history as avian influenza H7N9 is endemic in China.

Close contact with infected birds (e.g., farmer or visitor to a live market in endemic areas), or living in an area when avian influenza is endemic.

INVESTIGATIONS

RT-PCR: positive for H7-specific viral RNA.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Lack of residence in/travel history to an area with ongoing transmission, or lack of close contact with a suspected/confirmed case of COVID-19 in the 14 days prior to symptom onset.

Close contact with infected birds (e.g., farmer or visitor to a live market in endemic areas), or living in an area when avian influenza is endemic.

INVESTIGATIONS

RT-PCR: positive for H5N1 viral RNA.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Consider diagnosis in endemic areas, especially in patients who are immunocompromised.

History of symptoms is usually longer.

Presence of night sweats and weight loss may help to differentiate.

INVESTIGATIONS

Chest x-ray: fibronodular opacities in upper lobes with or without cavitation; atypical pattern includes opacities in middle or lower lobes, or hilar or paratracheal lymphadenopathy, and/or pleural effusion.

Sputum acid-fast bacilli smear and sputum culture: positive.

Molecular testing: positive for Mycoplasma tuberculosis.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Suspect neutropenic sepsis in patients with a history of recent systemic anticancer treatment who present with fever (with or without respiratory symptoms) as this can be rapid and life-threatening.[460]

Symptoms of COVID-19 and neutropenic sepsis may be difficult to differentiate at initial presentation.

INVESTIGATIONS

CBC: neutropenia.

RT-PCR: negative for SARS-CoV-2 viral RNA.

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