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  • Haemophilus influenzae is a small Gram-negative bacillus.

  • It is nonmotile.
  • Facultative anaerobe
  • Catalase and oxidase positive
  • Fastideous growth needs. Requires enrichments for growth.


  • Mucous membranes of the respiratory tract in humans.


  • The patient's own mucous membranes or transmitted patient-to-patient.


  • Haemophilus parainfluenzae and nonencapsulated H. influenzae typically colonize the upper respiratory tract in humans within the first few months of life. These bacteria typically cause sinusitis, otitis media, bronchitis, and pneumonia.
  • Encapsulated H. influenzae, primarily H. influenzae type b, is uncommon as normal flora of the upper respiratory tract but can be a common cause of serious infection in children.
  • Until immunization of children against H. influenzae type b became routine in developed countries, this bacterium was the most common cause of pneumonia, septicemia, meningitis, and epiglottitis in children under the age of four. Immunization has reduced the incidence of systemic infection by this bacterium 95%.

Clinical Disease

  • Haemophilus influenzae does not cause influenza. Influenza is a viral infection.
  • Haemophilus parainfluenzae and nonencapsulated H. influenzae typically cause sinusitis, otitis media, bronchitis, and pneumonia.
  • H. influenzae type b is the most common cause of pneumonia, septicemia, meningitis, epiglottitis, and cellulitis in children under the age of four who are not immunized.
  • One of the three most common causes of bacterial meningitis in addition to Strep. pneumoniae and N. meningitidis.
  • The H. influenzae type b (Hib) vaccine targets the polysaccharide capsule of H. influenzae type b

Primary Virulence Factors

  • Type b polysaccharide capsule:
    • most important factor in virulence
    • prevents destruction by innate immune response
    • can invade bloodstream directly from nasopharynx
  • Fimbriae for adherence
  • Neuraminidase (breaks down mucus) and IgA protease (destroys antibodies)

Additional Information:


From Haemophilus influenzae Infections, by Mark R Schleiss, MD, Associate Professor, Department of Pediatrics, Division of Infectious Diseases, University of Cincinnati and Children's Hospital Research Foundation.

Two Haemophilus influenzae Rd genes that complement the recA-like mutation rec-1.

Two Haemophilus influenzae Rd genes each complemented the pleiotropic defects of the recA-like mutation rec-1. One gene, fec, was isolated on a 3.6-kilobase-pair EcoRI restriction fragment by complementation of the Fec- phenotype of bacteriophage lambda. The other gene, rec, was identified on a 3.1-kilobase-pair EcoRI fragment by Southern hybridization by using recA-like gene probes from Erwinia carotovora and Pseudomonas aeruginosa PAO. In a rec-1 strain of H. influenzae, the cloned genes restored resistance to UV irradiation, transformation by chromosomal DNA, and spontaneous release of HP1 prophage to wild-type levels. The fec and rec genes were located on the cloned segments by insertion and deletion mutagenesis and subcloning. The restriction endonuclease cleavage maps of the two DNAs were similar but not identical. Southern hybridization demonstrated that the two EcoRI restriction fragments contained homologous DNA sequences, but a fec gene-specific probe was prepared. Each gene encoded a 38,000-dalton polypeptide. Haemophilus influenzae - Biology

A study of children was conducted in 3 Central Asian Republics. Approximately half of the Streptococcus pneumoniae isolates were serotypes included in available vaccine formulations. Approximately 6% of children carried Haemophilus influenzae type b (Hib). Using pneumococcal and Hib conjugate vaccines may decrease illness in the Central Asian Republics.

Streptococcus pneumoniae and Haemophilus influenzae cause a large percentage of acute respiratory and invasive bacterial infections throughout the world (1). Acute respiratory infection is the leading cause of childhood death in the Central Asian Republics of the former Soviet Union (2,3), a region that includes Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan, and the Kyrgyz Republic. These deaths occur despite the availability and use of antimicrobial drugs throughout the former Soviet Union (4,5).

To prevent illness from S. pneumoniae in the United States, the 7-valent pneumococcal conjugate vaccine (Prevnar, Wyeth Pharmaceuticals, Philadelphia, PA, USA) was added to the routine infant immunization schedule in 2000. Prevnar contains S. pneumoniae serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F. Higher valency formulations (9-, 11-, and 13-valent) are under evaluation. The 9-valent formulation (including types 1 and 5) was successful in South Africa (6) and The Gambia (7), and an 11-valent formulation (including types 1, 3, 5, and 7F) is being studied in the Philippines. An accelerated development and introduction plan for pneumococcal conjugate vaccines for use in developing countries is supported by the Global Alliance for Vaccines and Immunization (

H. influenzae type b (Hib) conjugate vaccines have been recommended for infants in the United States since 1990. Widespread use of these vaccines has dramatically reduced Hib invasive disease in both industrialized and developing countries (8,9). The World Health Organization (WHO) has recommended use of the Hib conjugate vaccine in regions of the world where the extent of Hib disease has been established. Prevalence of Hib invasive disease must be assessed in countries in the Central Asian Republics before introducing the Hib conjugate vaccine.

Laboratory data to determine prevalence of S. pneumoniae and Hib are not collected in the Central Asian Republics. To determine the benefits of using the pneumococcal and Hib conjugate vaccines in these countries, we conducted a nasopharyngeal swab survey of pediatric patients to identify the most prevalent serotypes and penicillin-resistance patterns of S. pneumoniae and to assess the presence of Hib.

The Study

In January 1997, we obtained nasopharyngeal swabs from a convenience sample of both ill and well children, ages 2–59 months, who were visiting outpatient clinics in Taraz City (formerly Djambul), Kazakhstan Fergana, Uzbekistan and Osh, Kyrgyz Republic. Before swabs were obtained, written parental consent was obtained in Russian, Kazak, Kyrgyz, or Uzbek under a protocol approved by a local institutional review board and the Centers for Disease Control and Prevention (CDC).

Nasopharyngeal swab collection and pathogen isolation have been described previously (1). Briefly, a flexible calcium alginate swab was inserted through the nares to the nasopharynx, rotated ≈180°, and withdrawn. While in the field, the swabs were first streaked on chocolate agar (CA) plates containing bacitracin to isolate H. influenzae, and then onto Trypticase soy 5% sheep blood agar plates containing gentamicin to isolate S. pneumoniae. All plates were brought back to the laboratory and incubated appropriately. Pure H. influenzae cultures were isolated and spread onto quad plates. Those colonies that grew on only the XV and blood quadrants were considered to be H. influenzae and were saved on CA slants. Suspected S. pneumoniae colonies were streaked onto conventional 5% sheep blood agar plates with an optochin disk added. After appropriate incubation, α-hemolytic isolates with an optochin inhibition zone >14 mm were considered to be S. pneumoniae and saved on CA slants. CA slants of both H. influenzae and S. pneumoniae were transported to CDC in Atlanta. Isolates of H. influenzae were serotyped with Difco H. influenzae serotype-specific rabbit antisera (BD, Sparks, MD, USA), and S. pneumoniae isolates were serotyped with CDC-prepared antiserum. S. pneumoniae cultures were tested for antimicrobial susceptibility to penicillin with broth dilution MIC testing by using the guidelines of the Clinical and Laboratory Standards Institute (formerly NCCLS) and customized MIC panels.

Results were similar in all 3 sites, so data were combined. The method of isolate storage and transport resulted in different survival rates among isolates (Tables 1 and 2). Low rates of S. pneumoniae isolates among children receiving antimicrobial drugs prevent any conclusions about that group. Among S. pneumoniae and H. influenzae isolates, survival was negatively associated with duration of storage. Among S. pneumoniae isolates, survival was positively associated with increasing age. However, the lack of any trends in Hib colonization and S. pneumoniae nonsusceptibility by age and duration of storage suggests that differential survival did not produce bias.

Of 630 children swabbed, 375 (59%) were colonized with S. pneumoniae. Of the 375 isolates, 224 S. pneumoniae isolates were available for susceptibility testing and serotyping. Of the 224 isolates, 54 (24%) were nonsusceptible to penicillin. The 9 most common serotypes in decreasing order were 19F (17% of isolates), 6B (15%), 6A (9%), 14 (6%), 23B (4%), 19A (3%), 23F (3%), 18C (2%), and 4 (2%). These accounted for 61% of all isolates.

In our sample, the 7-valent pneumococcal conjugate vaccine would cover 47% of pneumococcal isolates, the 9-valent would cover 48%, and the 11-valent would cover 51%. Of all the serotypes covered in these vaccines, serotypes 6B, 14, 19F, and 23F account for all nonsusceptible strains. Because all 3 vaccines contain these 4 serotypes, each vaccine would cover 33 (61%) of 54 nonsusceptible isolates of S. pneumoniae. An additional 13% of nonsusceptible strains are vaccine-related (strains 6A [4 of 54, 7%] and 23B [3 of 54, 6%]).

Of the 630 children from whom nasopharyngeal swabs were obtained, 357 (57%) were carrying H. influenzae. Of the 300 isolates available for serotyping, 34 (11%) were Hib. When Hib carriage is determined by multiplying the percentage of children colonized with H. influenzae times the percentage of Hib among all H. influenzae isolates tested, the carriage rate is 6% (Table 2).


Our survey showed that most children in these Central Asian Republics were colonized with at least 1 potential respiratory pathogen. Approximately half of the S. pneumoniae isolates and more than half of the penicillin-nonsusceptible S. pneumoniae isolates are included in the available pneumococcal conjugate vaccine formulations. Approximately 6% of the children in this convenience sample were carrying Hib.

The colonization rate of Hib found in our study is similar to rates observed in industrialized populations before Hib conjugate vaccines were widely used. Carriage rates for Hib before widespread vaccination in Finland, the United Kingdom, and the United States were 2%–6% (1013). In these countries, introduction of the Hib vaccine virtually eliminated Hib invasive disease (13).

Assessing the prevalence of disease due to specific respiratory pathogens is difficult blood cultures are insensitive, and other diagnostic tests are not specific. Nasopharyngeal colonization surveys of groups of children identify the predominant organisms circulating in the community and the presence or absence of antimicrobial-drug resistance. The presence of S. pneumoniae serotypes found in the pneumococcal conjugate vaccine suggests this vaccine may decrease some illness from acute respiratory infection. The experience in other countries with similar prevaccination Hib nasopharyngeal carriage rates suggests that the Hib conjugate vaccine may also decrease illness. These findings may be helpful in the decision-making process regarding the value of introducing conjugate vaccines for Hib and pneumococcal disease prevention.

Dr Factor was an Epidemic Intelligence Service officer in the Respiratory Diseases Branch of CDC when she led the field investigations in the Central Asian Republics. She is currently a medical epidemiologist in the CDC Bioterrorism Preparedness Response Program assigned to the New York City Department of Health and Mental Hygiene to develop emergency response plans for New York City.


Funding for this work was provided by the US Agency for International Development under a participating agency service agreement with CDC.

A Role in Chronic Obstructive Pulmonary Disease?

Noncapsulate Haemophilus influenzae is commonly found in the airways of patients with chronic obstructive pulmonary disease (COPD), both during stable disease and during exacerbations. Neutrophils are also found in large numbers in sputum from patients with COPD, which also contains released neutrophil products such as elastase. Why H. influenzae colonizes the lungs of patients with COPD in the presence of such large numbers of infiltrating neutrophils is not known. We set out to determine if abnormal interactions between H. influenzae and neutrophils could impact on COPD pathology. Noncapsulate H. influenzae clinical isolates were incubated in vitro with neutrophils from healthy volunteers, and respiratory burst activity, cytokine and chemokine production, phagocytosis and killing of bacteria, and neutrophil apoptosis and necrosis were measured. Neutrophil morphology was determined in sputum samples. H. influenzae were phagocytosed by neutrophils, thereby activating a respiratory burst and the secretion of the neutrophil chemoattractant IL-8. However, rather than kill the bacteria, the neutrophils themselves were killed (largely via necrosis) and released their granule contents into the extracellular environment. Neutrophil-derived IL-8, generated after the interaction of H. influenzae with neutrophils, may result in the further infiltration of neutrophils into the lungs, thereby amplifying the inflammatory response. However, the infiltrating neutrophils fail to kill the bacteria and instead release tissue-damaging products into the lung as they undergo necrosis. These results may help to explain the clinical picture in COPD.

Diseases of The Nervous System

Most damage is due to the Endotoxins that are released:

1) Endotoxins activates WBCs

3) Cytokines damage Blood Vessels causing:

---- Petechiae (small red/purple spots due to bleeding into skin)

Gram Negative - Capsule
Releases Endotoxins

Responsible for SPORADIC Cases

1) Type of Microorganism Responsible

2) Describe how it is contracted and what happens when it enters:

3) Length of Incubation Period

6) Eradicated Nations & Prevention

1) Virus enters tissue from SALIVA of BITING Animal
(or INHALATION of Saliva)

2) Virus very slowly REPLICATES in MUSCLE near bite

3) Virus then slowly moves up Peripheral Nerves and infects the CENTRAL NERVOUS SYSTEM as it ascends the spinal cord and enters the BRAIN

Infection of the Brain causes FATAL ENCEPHALITIS (inflammation for the brain)

Virus Enters SALIVARY GLANDS and other ORGANS

Weeks to Months - very long incubation period as it is slow to replicate

Brain of infected animal is studied with IMMUNOFLUORESCENCE Microscopy using a Fluorescent Antibody Stain (the infected animal is used to diagnose as it is very slow moving)

Since it is a virus, they also look for NEGRI BODIES(intracytoplasmic inclusions)

Post-Incidence Vaccine & Immune Globulin Serum

Rabies Vaccine - Human Diploid Cell Vaccine:
This can be given immediately after infected since the virus is slow to replicate.

Human Rabies Immune Globulin Serum:
This provides immediate antibodies until the body can respond to the vaccine by actively producing antibodies of its own.

the following Island Nations that are Free of Rabies:
Great Britain, Australia, New Zealand, Hawaii

Only strict vaccination policies and control over animal importation keep countries rabie-free

Most --> Fewest cases
Most: Wild Animals
Fewest: Domesticated Animals


Hepatic hydrothorax is defined as the presence of pleural fluid (usually greater than 500 mL) in a patient with cirrhosis in the absence of primary cardiac or pulmonary disease [5-7]. Hepatic hydrothorax occurs approximately 6&ndash13% of patients with advanced cirrhosis and is often associated with alcoholic liver cirrhosis [8-10]. Patients with cirrhosis and hepatic hydrothorax are prone to spontaneous infection of pleural fluid [1,11]. In general, cirrhosis is an immunocompromised state that increases a patient&rsquos susceptibility to the development of spontaneous bacterial infections and a variety of infections from uncommon pathogens [12,13]. SBEM is defined as infection of a preexisting hydrothorax in a patient with cirrhosis [1,11]. A diagnosis of SBEM is established if the pleural fluid cultures are positive and a polymorphonuclear count is >250 cells/&muL. The patient in this case report met both these criteria [11]. Low pleural fluid opsonic activity and C3 levels are found in patients with cirrhosis, who are at high risk of SBEM [14]. In our case, the route of H. influenzae to the pleural fluid was uncertain it was not clear whether it was from the respiratory tract or the gastrointestinal tract. Regarding liver cirrhosis, the major causative organisms of all bacterial infections are Gram-negative bacteria, while Gram-positive bacteria comprise about 20% and anaerobic bacteria only 3% [12]. A recent study reveals that Gram-positive cocci such as Staphylococcus, Enterococcus, and multi-resistant bacteria have become common pathogens [15]. Therefore, the etiology of bacterial infections in liver cirrhosis can be not only gastrointestinal tract sources but could also arise from other organs. The pathogenesis of SBEM, SBP, and spontaneous bacteremia is considered to be similar they share the same types of common pathogens [16]. In our case, we could not rule out complications of SBP, as the patient&rsquos ascites was too small to evaluate. However, SBEM can occur either with SBP (transdiaphragmatic spread) or without SBP (hematogenous spread) [16]. Therefore, it might be possible that bacteremia by H. influenzae results in SBEM. In previous reports, major causative microorganisms of SBEM were E. coli, Streptococcus species, Enterococcus species, and Klebsiella pneumonia [1,11]. These bacteria have been thought to originate from the gastrointestinal tract or to be systemic in origin [3]. Although H. influenzae is thought to be an indigenous microorganism in the respiratory tract, to our knowledge, there are no case reports of H. influenzae as a causative bacterium of SBEM [3]. Several reports reveal that H. influenzae is an indigenous bacterium in the human gastrointestinal tract [17- 19]. This fact might support that SBEM in this case occurred by the same pathway as the other major SBEM source. SBEM without ascites has been previously reported, and the pathogenic bacteria were E. coli, Pseudomonas stutzeri, and Enterococcus faecium [1]. If we take into account that H. influenzae is an indigenous bacterium of the intraperitoneal cavity, our case may support the hypothesis that enteric microorganisms reach the pleural fluid through bacteremia [1]. SBEM has a high recurrence rate (25-30%) and a poor prognosis [1]. For example, Xiol et al. reported that SBEM was fatal in 6 out of 16 cases [10]. Although SBEM is a rare common complication of liver cirrhosis, physicians should consider not only spontaneous bacterial peritonitis but also SBEM when a patient with cirrhosis and hydrothorax presents with infective symptoms such as fever and dyspnea. Moreover, these patients need to be intensively cared for because of their impaired immune systems, as they can very easily develop septic shock. In conclusion, we encountered a rare case of SBEM caused by H. influenzae. Our case suggests that it is essential to investigate the pathogenesis of hepatic hydrothorax in patients with cirrhosis as well as to offer systemic management and care for bacterial infections.

Watch the video: Haemophilus influenzae pathogenesis (February 2023).