Is Haemophilus influenzae (H. influenzae) an atypical bacterium?

From the Guidelines

No, Haemophilus influenzae is not typically considered an atypical bacterium. It is a fastidious, gram-negative coccobacillus that requires specific growth factors, such as X and V factors, to grow. Atypical bacteria are often used to describe organisms that do not fit into traditional categories, such as Mycoplasma or Chlamydia, which have different growth requirements and staining characteristics.

Key Characteristics of Haemophilus influenzae

• Haemophilus influenzae is usually susceptible to antibiotics such as amoxicillin-clavulanate, azithromycin, or ceftriaxone 1
• Treatment typically involves a 7-10 day course of one of these medications, depending on the specific infection and patient factors
• Some studies have reported high rates of susceptibility to certain antibiotics, such as cefuroxime, cefixime, and amoxicillin-clavulanate 1

Atypical Bacteria

• Atypical bacteria, such as Mycoplasma or Chlamydia, have different growth requirements and staining characteristics compared to Haemophilus influenzae 1
• These bacteria are often associated with mild CAP in young people and may require different diagnostic tests, such as serology or microimmunofluorescence (MIF) tests 1

Resistance Patterns

• Haemophilus influenzae can produce b-lactamase, which can affect its susceptibility to certain antibiotics, such as ampicillin 1
• Resistance to levofloxacin has increased significantly in Taiwan, from 2.0% in 2004 to 24.3% in 2010 1

From the Research

Definition of Atypical Bacteria

Atypical bacteria are those that do not conform to the typical characteristics of a particular species or group.

Characteristics of Haemophilus influenzae

• Haemophilus influenzae (H. influenzae) is a bacterium that can cause various infections, including respiratory tract infections, meningitis, and sepsis 2, 3, 4, 5, 6.
• There are two main types of H. influenzae: encapsulated (type b) and non-typeable (NTHi) 3, 4, 5.
• NTHi is considered a respiratory tract pathogen and is commonly associated with local infections such as otitis media, sinusitis, and bronchitis 3, 4, 5.
• However, NTHi can also cause invasive infections, including meningitis, bacteremia, and pneumonia 4, 5, 6.

Atypical Characteristics of Haemophilus influenzae

• The ability of NTHi to cause invasive infections, such as meningitis and ventriculitis, is considered atypical for a respiratory tract pathogen 4, 6.
• The emergence of multi-drug resistant NTHi strains is also a concern, making treatment more challenging 3, 6.
• The fact that NTHi can infect different patient populations, including adults and children, and cause a range of infections, from localized to systemic, makes it an atypical bacterium 2, 3, 4, 5, 6.

Evidence of Atypical Behavior

• A case report of a 53-year-old man who developed invasive NTHi infection associated with purpura fulminans and multiorgan failure highlights the atypical behavior of this bacterium 2.
• Another case report of a previously healthy patient who developed NTHi ventriculitis, a rare and severe presentation, further supports the atypical nature of this bacterium 6.