Fastidiosos

Haemophilus parainfluenzae

Pleomorphic Gram-negative coccobacilli

Identification & Growth

Identification

Requires only factor V (NAD) — grows without factor X, unlike H. influenzae

Growth Conditions

Chocolate agar, 35–37 °C, 5% CO₂, 24–48 h

Clinical Significance

Oropharyngeal flora; endocarditis (HACEK group) and respiratory tract infection

Intrinsic Resistance

Glycopeptides, clindamycin, fusidic acid and daptomycin have no activity

Bench Alerts

Usually a coloniser in sputum; significant in blood cultures and sterile material
Susceptibility testing on Mueller-Hinton Fastidious (MH-F) medium, per BrCAST/EUCAST

Clinical Notes

Clinical presentations

Member of the normal oropharyngeal microbiota, occasionally implicated in infective endocarditis as part of the HACEK group.
Cause of sinusitis, otitis media and lower respiratory infections, generally less virulent than H. influenzae.
Occasionally reported in abscesses, bacteremia and soft-tissue infections in the context of trauma or immunosuppression.

Specimens and collection

Serial blood cultures in suspected HACEK-group endocarditis, with prolonged incubation, as growth can be slow.
Sinus aspirate, tympanocentesis fluid or respiratory material according to the suspected site of infection.
Culture on chocolate agar supplemented with factors X and V, required for growth of this fastidious genus.

Epidemiology and at-risk populations

Routinely colonizes the human oropharynx; most isolates represent commensal flora with no pathological significance.
HACEK-group endocarditis predominantly affects patients with pre-existing structural valve disease or prosthetic valves.
Invasive infections are more frequent in young children and in patients with poor oral hygiene or periodontal disease.

Resistance and therapeutic implications

Beta-lactamase production is described in a proportion of isolates, compromising the activity of unprotected aminopenicillins.
Third-generation cephalosporins (such as ceftriaxone) are the mainstay of treatment for HACEK-group endocarditis, per infective endocarditis guidelines.
EUCAST publishes interpretive criteria for Haemophilus spp.; test for beta-lactamase production routinely before defining empirical therapy.

Bench and reporting notes

Pleomorphic Gram-negative coccobacillus, fastidious for growth factors X and/or V; dependence on factor V (but not X) differentiates H. parainfluenzae from H. influenzae.
Slow growth in blood culture can delay the diagnosis of endocarditis; communicate late growth compatible with HACEK to the clinician.
Clinical relevance of the isolate should be interpreted according to the collection site, as it is a usual oropharyngeal commensal.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Haemophilus parainfluenzae in the lab?

Haemophilus parainfluenzae is identified through requires only factor v (nad) — grows without factor x, unlike h. influenzae.

What are the intrinsic resistances of Haemophilus parainfluenzae?

This organism is naturally resistant to glycopeptides, clindamycin, fusidic acid and daptomycin have no activity. These drugs should not be reported as susceptible.

Where is Haemophilus parainfluenzae commonly found?

It is typically associated with oropharyngeal flora; endocarditis (hacek group) and respiratory tract infection.

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