[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/) › Haemophilus influenzae

[Microbiology](https://durgical.com/en/microbiology/) · [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/)

# Haemophilus influenzae

- Bacterium
- Gram-negative
- Droplet
- Exam priority: medium

A throat bacterium. Type b caused meningitis and epiglottitis in children before the vaccine; capsule-free strains cause ear and sinus infections.

Updated 2026-11-01

Also called: Hib, Haemophilus influenzae type b

## Key points

- Needs factors X and V: chocolate agar; satellitism around S. aureus on blood agar.
- Type b PRP capsule: the basis of the conjugate vaccine.
- Unvaccinated child with fever, drooling and tripod posture: epiglottitis; do not examine the throat until the airway is secured.
- Nontypeable strains: otitis, sinusitis, conjunctivitis and COPD flares; the vaccine does not cover them.
- Rifampicin prophylaxis for contacts of invasive Hib disease.

## At a glance

**Gram**
Gram-negative

**Shape**
Pleomorphic coccobacillus

**Oxygen**
Facultative anaerobe

**Family**
Pasteurellaceae

**Stain**
Gram: small red coccobacilli

## Morphology

- Small Gram-negative coccobacillus of variable shape
- Needs factor X (hemin) and factor V (NAD): grows on chocolate agar
- On blood agar it grows only around S. aureus colonies, which release factor V (satellitism)
- Six capsular types (a to f); type b is the most virulent. Nontypeable strains have no capsule

## Transmission

- Respiratory droplets and contact with secretions; healthy carriers are the usual source
- Birth canal to newborn
- Droplet (on top of standard) for invasive Hib disease until 24 hours of antibiotics

**Reservoir:** Humans only (nasopharynx)

### Isolation precautions

What the care team adds to standard precautions.

**Droplet**
Surgical mask within about a metre; single room.

## Virulence factors

- Type b polyribosyl-ribitol-phosphate (PRP) capsule: blocks phagocytosis and allows bloodstream invasion
- IgA protease: mucosal colonization
- Lipooligosaccharide: inflammation
- Some strains make beta-lactamase

## Diseases it causes

- Bacterial meningitis in young unvaccinated children (Hib) [Bacterial meningitis →](https://durgical.com/en/conditions/bacterial-meningitis/)
- Acute epiglottitis: an airway emergency [Acute epiglottitis →](https://durgical.com/en/conditions/acute-epiglottitis/)
- Acute otitis media (nontypeable strains) [Acute otitis media →](https://durgical.com/en/conditions/acute-otitis-media/)
- Acute sinusitis (nontypeable strains) [Acute rhinosinusitis →](https://durgical.com/en/conditions/acute-rhinosinusitis/)
- Pneumonia, and COPD exacerbations from nontypeable strains [Community-acquired pneumonia →](https://durgical.com/en/conditions/community-acquired-pneumonia/)

## Clinical picture

- Epiglottitis: high fever, drooling, muffled voice, painful swallowing and tripod posture; lateral neck film shows the "thumb sign"
- Also Hib cellulitis, septic arthritis and bacteremia
- Purulent conjunctivitis from nontypeable strains

## Diagnosis

- Culture of CSF, blood or secretions on chocolate agar
- Gram stain: Gram-negative coccobacilli
- Capsular antigen or PCR in CSF
- In epiglottitis, secure the airway before examining the throat

## Treatment

Invasive disease (meningitis, epiglottitis): third-generation cephalosporins such as ceftriaxone. Otitis and sinusitis: amoxicillin, or amoxicillin with clavulanic acid when beta-lactamase is present. Contacts of an invasive case get rifampicin chemoprophylaxis according to local rules.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)
- [Amoxicillin](https://durgical.com/en/pharmacology/amoxicillin/)
- [Rifampicin](https://durgical.com/en/pharmacology/rifampicin/)

## Prevention

- Hib conjugate vaccine (PRP linked to a carrier protein)
- Rifampicin chemoprophylaxis for selected contacts
- Droplet precautions in invasive disease

**Vaccine:** The Hib conjugate vaccine is in Colombia's PAI within the pentavalent (DTP, hepatitis B and Hib) or hexavalent vaccine, with a series in the first months of life and a booster. It does not protect against nontypeable strains.

## In Colombia

Thanks to PAI vaccination, Hib meningitis and epiglottitis are now uncommon in Colombia; bacterial meningitis is a notifiable event in SIVIGILA.

## Memory aid

"Haemophilus needs an X and a V": no growth without hemin (X) and NAD (V), and chocolate agar serves both.

## Test yourself

Think of the answer, then tap the question to see it.

## Which two growth factors does Haemophilus influenzae need?

Factor X (hemin) and factor V (NAD).

## What is Haemophilus satellitism?

On blood agar it grows only around S. aureus colonies, which release factor V and lyse red cells.

## Which Hib component is used in the conjugate vaccine?

The capsular polysaccharide polyribosyl-ribitol-phosphate (PRP), linked to a carrier protein.

## Which classic radiographic sign is seen in epiglottitis?

The "thumb sign": a swollen epiglottis on a lateral neck film.

## Why does the Hib vaccine not prevent most Haemophilus ear infections?

Those infections come from nontypeable strains, which lack the type b capsule the vaccine targets.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/microbiology/haemophilus-influenzae/)

## Related

- [Neisseria meningitidis](https://durgical.com/en/microbiology/neisseria-meningitidis/)
- [Moraxella catarrhalis](https://durgical.com/en/microbiology/moraxella-catarrhalis/)
- [Bordetella pertussis](https://durgical.com/en/microbiology/bordetella-pertussis/)

## Related conditions

- [Bacterial meningitis](https://durgical.com/en/conditions/bacterial-meningitis/)
- [Acute epiglottitis](https://durgical.com/en/conditions/acute-epiglottitis/)
- [Acute otitis media](https://durgical.com/en/conditions/acute-otitis-media/)
- [Acute rhinosinusitis](https://durgical.com/en/conditions/acute-rhinosinusitis/)
- [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

**Droplet**
Surgical mask within about a metre; single room.

**Airborne**
N95 respirator and a negative-pressure room.

[← Back to the group: Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Chapter 8: Haemophilus influenzae](https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-8-haemophilus-influenzae.html) (CDC, 2024); [About Haemophilus influenzae Disease](https://www.cdc.gov/hi-disease/about/index.html) (CDC, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/haemophilus-influenzae/