Differentials

Coronavirus disease 2019 (COVID-19)

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.[102]

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.

Bacterial pneumonia

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

In addition to cough and fever there may be pleuritic chest pain, dyspnoea, and sputum production that may be mucopurulent.

INVESTIGATIONS

CXR: common finding is a lobar consolidation.

Blood culture: positive for infecting organism.

Sputum culture: growth of infecting organism.

Rhinovirus infection

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Common cause of respiratory tract infections. Presents mostly with upper respiratory symptoms but can cause severe acute respiratory distress and is more severe in patients with underlying chronic lung disease.

INVESTIGATIONS

Testing is not routinely recommended for rhinovirus. However, reverse transcription polymerase chain reaction (RT-PCR) can be performed in hospitalised patients.

Respiratory syncytial virus (RSV) infection

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Most common cause of lower respiratory tract infection in children <1 year.[103]

Also a significant and often unrecognised cause of lower respiratory tract infection in both older and immunosuppressed patients.[104]

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

Characterised by seasonal outbreaks. In the northern hemisphere, these usually occur from November to April, with a peak in January or February. In the southern hemisphere, wintertime outbreaks occur from May to September, with a peak in May, June, or July. In tropical and semi-tropical climates, the seasonal outbreaks are usually associated with the rainy season.[105]

INVESTIGATIONS

Reverse transcription polymerase chain reaction (RT-PCR): positive for RSV.

Culture: positive for RSV (not generally useful in the clinical setting given long turnaround time).

Laboratory testing is not routinely recommended for RSV.[106] 

Parainfluenza virus infection (PIV)

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

An important respiratory pathogen in adults and children; the second most common cause, after respiratory syncytial virus, of acute lower respiratory tract infections in infants and young children.[107]

In adults, generally causes mild upper respiratory tract infections, but can induce life-threatening lower respiratory tract infections in immunocompromised patients.[108]

The seasonal patterns of PIV infection in the US have changed over the past few decades. After 1962, PIV-1 and PIV-2 began to present in epidemics, and currently appear every 2 years in the autumn. In comparison, PIV-3 occurs in annual spring epidemics, whereas seasonal patterns of PIV-4 infections have been difficult to establish, since the disease is usually mild and the virus is difficult to detect. In developing and tropical countries, parainfluenza viruses do not show seasonal variations.[109]

INVESTIGATIONS

Reverse transcription polymerase chain reaction (RT-PCR): positive for parainfluenza virus.

Viral culture: positive for parainfluenza virus.

Meningococcal disease/septicaemia

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

May present with non-specific respiratory signs/symptoms. May present with triad of tachycardia, low blood pressure, and high fever.

As the illness develops, thirst, respiratory distress, a petechial rash, peripheral vasoconstriction, altered consciousness, photophobia, hypotonia, neck stiffness, seizures, and tachycardia may be present.

In infants, a bulging fontanelle and a characteristic high-pitched cry may occur.

A positive Kernig's or Brudzinski's sign indicates meningeal inflammation and is suggestive of meningitis; present only in a minority of patients.

INVESTIGATIONS

Polymerase chain reaction of blood or cerebrospinal fluid (CSF) can detect meningococcal DNA.

Isolation of Neisseria meningitidis from a sterile body site (blood, CSF, joint, pleural fluid, pericardial fluid, or aspiration or biopsy of a purpuric lesion) is the definitive test for diagnosis of invasive meningococcal infections.

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