Haemophilus influenzae Explained: Causes, Symptoms, and Prevention

Introduction OF Genus Haemophilus

Gram negative rods, coccobacilli, Non motile, non-spore forming, variable Catalase rxn. Microaerophilic, humid enriched environment.  Requires medium supplemented with growth stimulating factor (X and/or V factor).  Causes Respiratory, genitourinary, and CNS infection.  Species with prefix Para – require V factor only for growth.

Medically Important Species:

•  H. influenzae

•  H. parainfluenzae

•  H. haemolyticus

•  H. parahaemolyticus

•  H. ducreyi

•  H. aegypticus

•  H. aphrophilus

•  H. segnis

•  H. paraphrophilus

1. Haemophilus influenzae:

A slender , short, non motile, non-sporing, non acid fast gram negative coccobacilli.  H. influenzae occurs in capsulate and non-capsulate form Based on polysaccharide capsule type, capsulated H. influenzae can be classified in to six serotype: a, b, c, d, e, and f.  b serotype is highly virulent.  Non capsulated (Non-typable) H. influenza are less pathogenic. Haemophilus influenzae was first discovered in 1892 by Richard Pfeiffer, a german physician and bacteriologist. The bacterium is an important pathogen and can couse various infections, especially in children. Haemophilus influenzae is bacterium that can cause a range of infections. The routes of infection and transmission for H. influenzae include: respiratory transmission: the primary route of H. influenzae transmission is through respiratory droplets.an infected person can spread the bacteria by coughing or sneezing, and others can become infected by inhaling these droplets or by coming into contact with surfaces or objects contaminated by the droplets and then touching their nose or mouth. H.influenzae can colonize the upper respiratory tract without causing disease. This means that people can carry the bacteria in their nose and throat without showing any symptoms, and these carries can potentially spread the bacterium to others. 

 

Virulence factor of haemophilus influenzae

• Capsular polysaccharide has antiphagocytic activity.

• Adherence (fimbiae).

• Membrane lipooligosaccharide may be responsible in bacterial attachment invasiveness.

• IgA protease is  Facilitating attachment to the respiratory mucosa

Pathogenesis and Clinical manifestation

In developing countries invasive infections with capsular type b H. influenzae are major causes of ill health and premature death in infants and young children.  Infections are usually bacteraemic. H. influenzae type b causes:  Pyogenic (purulent) meningitis in young children below 5 year.  Pneumonia and empyema (mainly adults).  Acute epiglottitis (acute inflammatory swelling of the epiglottis and neighbouring structures) which may cause fatal airway obstruction.  Cellulitis (orbital), Osteomyelitis, septic arthritis, and occasionally other invasive infections. Non-typable H. influenzae strains are mainly responsible for chronic bronchitis (usually in adults), Middle ear infections, paranasal sinusitis and conjunctivitis. These strains form part of the normal microbial flora of the upper respiratory tract in 50–75% of persons. H influenzae type b enters by way of the respiratory tract.  H influenzae type b is one of the most common etiologic agents of bacterial otitis media and acute sinusitis.  The organisms may reach the bloodstream and be carried to the meninges or, less frequently, may establish themselves in the joints to produce septic arthritis.

Risk factors

Some factors increase the risk of H.influenzae infection, including certain medical conditions, age (children, especially those under 5, are more susceptible)., and environmental factors like living in crowded conditions. The risk factors for Haemophilus influenzae infection, particularly for the severe, invasive forms of the disease, vary depending on the patient's age and the specific strain of the bacteria (Type b or Non-Typeable).

Haw to diagnosis H.influenzae

Specimens: These include cerebrospinal fluid (c.s.f.), nasopharyngeal specimens, pus, and blood for smears and cultures.  Specimens must be cultured as soon as possible and not refrigerated.  It is best stained using dilute carbol fuchsin as the counter stain.  The capsule which surrounds capsulated strains can be demonstrated by using specific antiserum. Culture: H. influenzae grows poorly anaerobically.  Growth is best achieved in a moist carbon dioxide enriched atmosphere. The temperature range of growth is 20–40 ºC with an optimum of 35 37 ºC.  Needs an essential growth factors namely X & V present in blood. Chocolate agar: capsulated H. influenzae strains produce mucoid colonies.  Cultures have a distinctive smell, H. influenzae grows well on chocolate agar because it contains factors X and V. Heating blood agar to 75 ºC inactivates serum NADase and releases extra factor V from the red cells. Addition of bacitracin (300 mg/litre) provides a selective medium to recover H. influenzae from sputum. This is not needed when culturing c.s.f.

Treatment of haempphilus influenzae

• susceptible to ampicillin.

• All strains are susceptible to cephalosporins.

• Prompt diagnosis is required.

Haw to prevention H.influenzae

Contact with patients suffering from H influenzae clinical infection poses little risk for adults. But presents a definite risk for nonimmune siblings and other nonimmune children under age 4 years who are close contacts.  Prophylaxis with rifampin is recommended for such children. The hib vaccine (haemophilus influenzae type b vaccine) has been highly effective in preventing infections caused by H.influenzae type b, which was historically the most common cause of bacterial meningitis in children. The vaccine does not protect against other non-b serotypes or nontypeable strains of H.influenzae. proper hygiene practices, like handwashing, can help reduce the spread of the bacterium.

Conclusion

Haemophilus influenzae is an important human pathogen that can cause a wide range of infections, from mild respiratory tract illnesses to severe invasive diseases such as meningitis, pneumonia, and septicemia. The introduction of the H. influenzae type b (Hib) vaccine has significantly reduced the global burden of invasive Hib infections, especially in children. However, non-typeable strains and other serotypes remain a public health concern. Continued vaccination efforts, early diagnosis, appropriate antibiotic treatment, and surveillance are crucial to control the spread and impact of this pathogen.