Differentials
Human metapneumovirus
SIGNS / SYMPTOMS
Produces a clinical syndrome that closely mimics RSV. May be clinically indistinguishable.[110]
INVESTIGATIONS
Polymerase chain reaction positive for metapneumovirus.
Influenza virus
SIGNS / SYMPTOMS
Accounts for 1% to 24% of bronchiolitis.[111][112] Closely mimics RSV in presentation. Fever frequently >101.9°F (38.9°C). Coryza frequently present. Greater frequency of pneumonia and bacterial superinfection than RSV.
INVESTIGATIONS
CXR may show infiltrates.
Polymerase chain reaction: positive for influenza virus
Rapid testing by immunoassay or viral neuraminidase detection: positive for influenza virus.
Enzyme-linked immunosorbent assay and viral culture: positive for influenza virus.
Parainfluenza virus
SIGNS / SYMPTOMS
Accounts for 10% to 30% of bronchiolitis. Parainfluenza type III closely mimics RSV in presentation. Presence of coryza is associated with parainfluenza infection. Parainfluenza type III often occurs in late spring after peak RSV circulation.
INVESTIGATIONS
Enzyme-linked immunosorbent assay and polymerase chain reaction testing: positive for parainfluenza virus.
Viral culture: positive for parainfluenza virus (standard test).
Bacterial pneumonia
SIGNS / SYMPTOMS
Bacterial infections are not associated with wheeze and generally cause higher fevers than RSV.[101]
Fever >103.9°F (40°C).
INVESTIGATIONS
CXR: lobar infiltrate
WBC count: elevated with left shift suggests an active bacterial process.
Neonatal sepsis
SIGNS / SYMPTOMS
Often presents with a history of poor feeding and elevated work of breathing (similarly to RSV infection in infants), decreased level of consciousness, decreased urine output, apnea, temperature instability, shock.
INVESTIGATIONS
Cultures: blood, urine, and cerebrospinal fluid may detect infective organisms or may be normal.
ABG may show respiratory and/or metabolic acidosis, hypoxemia.
Enterovirus-D68 (EV-D68)
SIGNS / SYMPTOMS
Produces a clinical syndrome similar to that of the common cold. May cause severe respiratory illness with signs and symptoms of pneumonia. Although EV-D68 causes primarily respiratory illness, systemic disease occurs, especially neurologic involvement.
INVESTIGATIONS
Many clinical laboratories use real-time polymerase chain reaction assays designed to detect both rhinoviruses and enteroviruses, but these tests do not distinguish between the species. Most clinical laboratories do not routinely perform viral sequence analysis to specifically identify EV-D68, but this test may be obtained through state health departments and the Centers for Disease Control on a case-by-case basis.
Coronavirus disease 2019 (COVID-19)
SIGNS / SYMPTOMS
COVID-19 may present as bronchiolitis in some infants. It may cause fever, coryza, and cough as well as acute gastroenteritis.
INVESTIGATIONS
Real-time reverse transcription polymerase chain reaction (RT-PCR): positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA.
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