Co-infection with Human Metapneumovirus and Group A Streptococcal Pharyngitis in School-Age Children
A school-age child can simultaneously harbor human metapneumovirus (hMPV) as a true respiratory pathogen causing viral pharyngitis while also carrying or being infected with Group A Streptococcus (GAS), because viral respiratory infections and bacterial pharyngitis frequently overlap in the 5–15 year age group, and neither infection confers protection against the other.
Why This Co-infection Occurs
Epidemiological Overlap
hMPV is a major respiratory pathogen in children, responsible for 5–10% of hospitalizations for acute respiratory tract infections, with peak incidence in young children but continuing throughout childhood 1, 2, 3.
GAS pharyngitis primarily affects children aged 5–15 years, accounting for 20–30% of acute pharyngitis cases in this age group, with peak incidence in winter and early spring 4.
Both pathogens circulate during the same seasonal window (winter and early spring in temperate climates), creating frequent opportunities for co-infection 4, 1.
Viral-Bacterial Interaction Mechanisms
Viral respiratory infections damage the pharyngeal epithelium, potentially facilitating secondary bacterial colonization or invasion by GAS 5.
hMPV causes upper and lower respiratory tract infections with symptoms including rhinorrhea, nasal congestion, cough, and fever—clinical features that do not prevent concurrent bacterial pharyngitis 6, 3.
Nearly every child is infected with hMPV by age 5, and re-infections occur throughout life because immunity is incomplete, meaning school-age children remain susceptible to hMPV even while exposed to GAS 3.
The Carrier State Complicates Diagnosis
10–15% of school-age children are asymptomatic GAS carriers, meaning they harbor GAS in the throat without active infection 4.
A child with symptomatic hMPV infection may simultaneously be a GAS carrier, yielding positive GAS testing (RADT or culture) even though the acute illness is viral 4.
Conversely, a child with true GAS pharyngitis may have concurrent hMPV detected by PCR, representing either co-infection or recent viral shedding 5, 1.
Clinical Implications
Diagnostic Challenges
Clinical features of hMPV and GAS pharyngitis overlap significantly: both can cause sore throat, fever, and pharyngeal erythema, making differentiation impossible on clinical grounds alone 4, 3.
The presence of cough, rhinorrhea, hoarseness, or conjunctivitis strongly suggests viral (hMPV) etiology and should prompt caution before attributing symptoms solely to GAS 4.
Microbiological confirmation is mandatory for GAS diagnosis (RADT or throat culture), but a positive result does not exclude concurrent viral infection 4.
When to Suspect Co-infection
A child with positive GAS testing who also has prominent cough, rhinorrhea, or lower respiratory symptoms likely has concurrent hMPV or another respiratory virus 4, 7, 3.
hMPV/RSV co-infections are common (occurring in up to 48.7% of hMPV cases in one study), suggesting that multiple respiratory pathogens frequently circulate together 5.
Children hospitalized with severe respiratory illness may have hMPV detected alongside bacterial pathogens, with co-infection potentially increasing disease severity 5.
Management Approach
Testing Strategy
Perform RADT or throat culture for GAS when fever, tonsillar exudates, tender anterior cervical nodes, and absence of viral features are present 4.
In children and adolescents, a negative RADT must be followed by throat culture to avoid missing true GAS infection 4.
Do not test for GAS when obvious viral features dominate (cough, rhinorrhea, conjunctivitis), as this leads to false-positive results from asymptomatic carriage 4, 8.
Treatment Decisions
Treat confirmed GAS pharyngitis (positive RADT or culture) with penicillin V or amoxicillin for 10 days, regardless of concurrent viral symptoms, to prevent acute rheumatic fever and suppurative complications 4.
Provide supportive care for viral symptoms (analgesics, hydration, rest) even when treating GAS, as antibiotics do not address the viral component 4, 8.
Antibiotics shorten GAS symptom duration by only 1–2 days, so persistent cough, rhinorrhea, or lower respiratory symptoms after starting antibiotics likely reflect ongoing viral infection 4, 8.
Common Pitfalls to Avoid
Testing for GAS in a child with clear viral features (cough, rhinorrhea, conjunctivitis) will detect asymptomatic carriers and lead to unnecessary antibiotics 4, 8.
Assuming all pharyngitis with positive GAS testing requires antibiotics ignores the possibility that the child is a carrier with intercurrent viral pharyngitis 4.
Failing to recognize that hMPV symptoms (cough, rhinorrhea, fever) can persist for 7–10 days even with appropriate GAS treatment, because the viral infection follows its own natural course 6, 3.
Not considering hMPV or other respiratory viruses when a child with "treated strep throat" remains symptomatic, as the initial diagnosis may have been a viral illness in a GAS carrier 4, 3.