Haemophilus Influenzae Infections

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Questions and Answers

What is the primary mode of transmission for Haemophilus influenzae?

Sexual transmission

Direct contact with contaminated surfaces

Respiratory secretions (correct)

Ingestion of contaminated food

Which factor is NOT essential for the virulence of nontypeable Haemophilus influenzae (NTHi)?

Cell surface factors

Pili

Bacterial attachment to epithelial cells

Capsule production (correct)

Which disease is primarily caused by Haemophilus ducreyi?

Chancroid (correct)

Otitis media

Meningitis

Sinusitis

Which of the following infections is commonly associated with nontypeable Haemophilus influenzae (NTHi)?

Otitis media Signup and view all the answers

The most serious infections caused by Haemophilus influenzae type b belong to which biotypes?

I and II Signup and view all the answers

Which specific population is particularly at risk for Brazilian purpuric fever caused by Haemophilus influenzae?

Children between ages 1 and 4 Signup and view all the answers

Which agar is optimal for the growth of Haemophilus spp.?

Chocolate agar Signup and view all the answers

Which of the following does NOT predispose an individual to infection with nontypeable Haemophilus influenzae (NTHi)?

Poor hygiene Signup and view all the answers

What is the primary reason Haemophilus spp. do not grow on 5% sheep blood agar?

Lack of NAD (V factor) Signup and view all the answers

Which phenomenon allows Haemophilus spp. to grow in proximity to Staphylococcus aureus on sheep blood agar?

Satellite phenomenon Signup and view all the answers

Which component is likely involved in the attachment and penetration of host epithelial cells by Haemophilus ducreyi?

Toxins Signup and view all the answers

Which of the following drugs is part of the recommended treatment for life-threatening infections caused by H. influenzae?

Cefotaxime Signup and view all the answers

Which alternative drug can be used to treat invasive H. influenzae infection if the recommended drugs are not available?

Imipenem Signup and view all the answers

What visual cue indicates a positive Satellitism test in the provided image?

Growth of Haemophilus around Staphylococcus aureus Signup and view all the answers

Which specimens are typically used for smears and cultures of Haemophilus spp.?

Expectorated sputum and respiratory specimens Signup and view all the answers

Why might centrifugation be used when preparing a body fluid specimen for Gram stain examination?

To concentrate the specimen by depositing material at the bottom of the tube Signup and view all the answers

What is a challenge in detecting Haemophilus spp. in Gram stains of clinical specimens?

They stain a pale pink and may blend with the pink proteinaceous background Signup and view all the answers

What type of assay is used to directly detect Haemophilus influenzae type b capsular polysaccharide in clinical specimens?

Particle agglutination Signup and view all the answers

For what types of samples has a PCR been developed to detect H. influenzae capsular types a and f?

CSF, plasma, serum, and whole blood Signup and view all the answers

What incubation conditions stimulate growth of most strains of Haemophilus spp.?

5% to 10% CO2 Signup and view all the answers

What characteristic is used to identify encapsulated strains of Haemophilus influenzae on chocolate agar?

Tan mucoid colonies Signup and view all the answers

Which method is especially useful for detecting H. influenzae in patient therapy and outbreaks?

PCR Signup and view all the answers

What is required by species of the genus Haemophilus for in vitro growth?

Protoporphyrin IX and NAD or NADP Signup and view all the answers

Which Haemophilus species is only found in humans during infection?

Haemophilus ducreyi Signup and view all the answers

What is the typical cellular shape of Haemophilus species?

Coccobacillary or short rods Signup and view all the answers

What atmosphere enhances the growth of Haemophilus species?

5-7% CO2 Signup and view all the answers

Where is Haemophilus influenzae typically found in the human body?

Upper respiratory tract Signup and view all the answers

How is Haemophilus ducreyi typically transmitted?

Sexual contact Signup and view all the answers

What type of microorganisms are in the genus Haemophilus?

Gram-negative bacilli Signup and view all the answers

Which Haemophilus species mainly uses endogenous strains for transmission?

Haemophilus influenzae Signup and view all the answers

Study Notes

Pathogenesis and Spectrum of Disease

Production of a capsule and factors that mediate bacterial attachment to human epithelial cells are the primary virulence factors associated with Haemophilus spp.
Infections caused by H. influenzae are often systemic and life-threatening, whereas infections caused by nontypeable (do not have a capsule) strains are usually localized.
Most serious infections caused by H. influenzae type b are biotypes I and II.
Most H. influenzae infections are now caused by nontypeable strains (NTHi).
Transmission is often via respiratory secretions.
The organism is able to gain access to sterile sites from colonization in the upper respiratory tract.
Clinical infections include otitis media, sinusitis, bronchitis, pneumonia, and conjunctivitis.
Immunodeficiencies and chronic respiratory problems may predispose an individual to infection with NTHi.
Chancroid is the sexually transmitted disease caused by H. ducreyi.

General Characteristics

The genus Haemophilus contains significant genetic diversity.
Members of the genus are small, nonmotile, pleomorphic gram-negative bacilli.
The cells are typically coccobacillary or short rods.
Species of the genus Haemophilus require protoporphyrin IX (X factor) and V factor (NAD or NADP) for in vitro growth.
Haemophilus spp. are facultative anaerobes enhanced in a 5% to 7% CO2-enriched atmosphere.

Epidemiology

Haemophilus spp. normally inhabit the upper respiratory tract of humans.
Asymptomatic colonization with H. influenzae type b is rare.
H. ducreyi is only found in humans, and its presence in clinical specimens indicates infection.

Laboratory Diagnosis

Specimens consist of expectorated sputum and other types of respiratory specimens, pus, blood, and spinal fluid.
Direct Gram stain examination of body fluid specimens may be performed after centrifugation.
Gram stains of the smears from clinical specimens must be examined carefully.
Haemophilus spp. stain a pale pink and may be difficult to detect in the pink background of proteinaceous material often found in clinical specimens.
Antigen detection can be performed using commercially available particle agglutination assays.
Molecular methods such as PCR can be used for rapid detection.

Cultivation / Media of Choice

Haemophilus spp. typically grow on chocolate agar as smooth, flat or convex, buff or slightly yellow colonies.
Chocolate agar provides hemin (X factor) and NAD (V factor), necessary for the growth of Haemophilus spp.
The satellite phenomenon may be observed on sheep blood agar, where tiny colonies of Haemophilus spp. grow near colonies of bacteria capable of producing V factor.

Treatment

Invasive H. influenzae infection often requires hospitalization.
The current recommended treatment of life-threatening illness caused by H. influenzae is cefotaxime or ceftriaxone.
Alternative drugs include trimethoprim-sulfamethoxazole, imipenem, and ciprofloxacin.

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Description

Understand the pathogenesis and spectrum of disease caused by Haemophilus influenzae, including the role of virulence factors and types of infections.