S1B5 - Haemophilus Flashcards
Of the following diseases, which is least likely to be caused by H. influenzae type B?
A) Cellulitis
B) Otitis media
C) Epiglottitis
D) Pneumonia
E) Meningitis
Cellulitis
Answer Explanation
Hib can cause all of these diseases except for cellulitis. Prior to vaccination, it was a leading cause of septic arthritis in infants. In the modern era, it is the least likely disease (of the answer choices) to be caused by Hib. In part, this is because the nonencapsulated forms only rarely cause septic arthritis.
Epiglottitis, meningitis, and pneumonia are still often caused by H. flu, especially in adults who did not receive the vaccine. H. flu otitis media is usually caused by nonencapsulated strains, which are not covered by the vaccine.
How is H. influenzae transmitted? What patient populations are most at risk?
H. influenzae is transmitted via aerosol droplets and often occurs in immunocompromised individuals such as asplenic patients and children after maternal antibody protection has declined.
Where does H. influenzae colonize? What virulence factor allows it to spread within the body?
H. influenzae colonizes the upper respiratory tract and is protected from IgA by IgA protease. It can cause local inflammation, or encapsulated strains can invade the submucosa and spread by bloodstream to seed in the CNS, large joints, or soft tissue.
Is H. influenzae encapsulated? Which strain of H. influenzae is the most virulent?
H. influenzae has six strains that have capsules. Haemophilus influenzae type B is the most virulent, causing 95% of pediatric infections and 50% of adult infections.
Currently, it is recommended that close contacts of patients with confirmed Hemophilus influenzae infections receive chemoprophylaxis. What mode of transmission is involved?
A) Direct contact
B) Respiratory tract droplets
C) Vertical transmission
D) Fecal-oral
E) Sexual contact
Respiratory tract droplets
Answer Explanation
H. influenzae can be transmitted via droplets, direct contact, and vertical transmission. Droplet transmission is the primary method; direct contact transmission is of limited contagiousness, and vertical transmission occurs between mother and neonate. It is not transmitted in fecal-oral or sexual fashion.
What media does H. influenzae grow on?
H. influenzae is a fastidious organism and grows on chocolate agar (heat inactivated blood) that has factors V (NAD) and X (hematin) from lysed red blood cells.
What diseases does H. influenzae cause?
HAEMOPhilus causes:
- septic Arthritis
- Epiglottitis
- Meningitis
- Otitis media
- Pneumonia
It is also a common cause of bacterial conjunctivitis and sinusitis.
What is prophylactic treatment for close contacts of individuals infected with H. influenzae?
Rifampin prophylaxis is used for close contacts with infected individuals.
Which is the most accurate description of the Hemophilus influenzae type B vaccine?
A) Composed of purified type B capsular polysaccharide
B) Contains factor X
C) Unnecessary with rifampin prophylaxis
D) Consists of purified surface antigen
E) Polyribosyl ribitol phosphate capsule covalently linked to a carrier protein
Polyribosyl ribitol phosphate capsule covalently linked to a carrier protein
Answer Explanation
The Hib vaccine is a conjugate vaccine in which the capsule is covalently linked to a carrier protein. This induces high levels of antibody (mainly IgG) production. The previous generation of vaccine was composed of purified type B capsular polysaccharide. Rifampin is used to prophylaxis close contacts of patients with invasive Hib infections, but is not a means of vaccination. Factor X is needed to culture H. flu, but is not related to the vaccine.
A child who was vaccinated for H. influenzae presents to the doctor with otitis media. Cultures are positive for H. influenzae. What is the most likely reason for this result?
Unencapsulated and therefore untypeable strains of H. influenzae exist and can also cause disease, especially diseases of the upper respiratory tract such as non-invasive sinusitis and otitis media.
What are the 2 components of the vaccine for H. influenzae type B?
Haemophilus influenzae type B vaccine is available, which is a capsular polysaccharide of the type B strain conjugated to diphtheria toxoid.
Which is primary treatment for H. influenzae type B meningitis?
A) Haemophilus B vaccine
B) Ampicillin
C) Ceftriaxone
D) Rifampin
E) Penicillin G
Ceftriaxone
Answer Explanation
3rd-generation cephalosporins like ceftriaxone and cefotaxime are the mainstay treatments for H. flu infections. This is because they are strongly bactericidal and penetrate the subarachnoid space, most important for meningitis. Ampicillin can also be used, but has relatively high levels of resistance. The vaccine is not used to treat infections. Rifampin is used to prophylax close contacts of patients infected with H. flu type B.
Which capsular polysaccharide is used in the Haemophilus influenzae type B vaccine?
The capsular polysaccharide used in the Haemophilus influenzae type B vaccine is polyribosylribitol phosphate (PRP).
Does H. influenzae produce a positive or negative Quellung reaction?
H. influenzae produces a positive Quellung reaction, where antibodies bind to the bacterial capsule and the result can be visualized under a microscope.
Which chemoprophylaxis should be given to close contacts of a patient with H. influenzae type B pneumonia?
A) Ceftriaxone
B) Rifampin
C) Ampicillin
D) Levofloxacin
E) Dexamethasone
Rifampin
Answer Explanation
Close contacts of a patient with Hib infection should receive rifampin. Ceftriaxone and ampicillin can be used to treat Hib infections (although ampicillin has a high degree of resistance). Dexamethasone is a glucocorticoid that inhibits the inflammatory response. Levofloxacin isn’t used to treat H. flu infections.
What antibiotics are used to treat H. influenzae?
Treatment for H. influenzae includes a third generation cephalosporin (e.g. ceftriaxone) for meningitis and amoxicillin for mucosal infections.
What is the morphology and gram staining of Haemophilus influenzae?
Haemophilus influenzae is a gram-negative coccobacilli.
Which external factors are required for growth of Hemophilus influenzae on lab media?
A) Factors V and II
B) Factors X, V and II
C) Factor V
D) Factor X
E) Factors X and V
Factors X and V
Answer Explanation
H. flu requires factors X (hematin) and V (NAD) for growth. When grown on chocolate agar, H. flu lyses the erythrocytes to release those factors. Factor X is essential for the function of electron-transport chain enzymes (aerobic metabolism). H. flu lacks some enzymes necessary for de novo synthesis of NAD. Factor II is prothrombin and plays no role in H. flu metabolism.
What bacterial species grows on chocolate agar but not on blood agar?
Haemophilus species grow on chocolate but not on blood agar.
Below is a description of what disease caused by what bug?
- 1st recognized in a rural Brazilian town in 1984.
- A fulminant pediatric disease -initially conjunctivitis.
- Days to weeks later –high fever, vomiting, abdominal pain.
- In 12-48 h (if untreated) –petechiae, purpura, shock death
DISEASES BY OTHER HAEMOPHILUS SPECIES
Brazilian purpuric fever
- Caused by H. influenzae biogroup aegyptius
- 1st recognized in a rural Brazilian town in 1984.
- A fulminant pediatric disease -initially conjunctivitis.
- Days to weeks later –high fever, vomiting, abdominal pain.
- In 12-48 h (if untreated) –petechiae, purpura, shock death
Below is a description of what disease caused by what bug?
- Genital ulcers and inguinal lymphadenitis.
- Less common in US but frequent in developing nations.
- Acquired after a break in epithelium during sexual contact.
- In 4-7d –a papule develops with surrounding edema
Disease (H. ducreyi) –Chancroid:
- Genital ulcers and inguinal lymphadenitis.
- Less common in US but frequent in developing nations.
- Acquired after a break in epithelium during sexual contact.
- In 4-7d –a papule develops with surrounding edema
Below is a description of what species of bacteria?
- Gram (-)ve small rods; normal flora of URT & oral cavity.
- Fastidious but can grow slowly on blood agar.
- H. parainfluenzaeconstitutes 10% of bacteria in saliva
HACEK species
- H. parainfluenzae
- H. aphrophilus
- H. paraphrophilus
- Aggregatibacter actinomycetemcomitans
- Cardiobacterium hominis
- Eikenella corrodens
- Kingella kingae(septic arthritis in children <24mo).
What clinical features support the diagnosis of pertussis?
Pertussis is a clinical diagnosis. Features suggestive of pertussis include a cough lasting more than 2 weeks and characterized by paroxysms of coughing or an inspiratory whoop.
What lab finding supports the diagnosis of pertussis?
Labs showing an absolute lymphocytosis due to the presence of pertussis toxin can support a clinical diagnosis of pertussis. In addition, hypoglycemia may be seen due to the increased insulin secretion (from increased cAMP concentration).
What agents are used for the treatment and prophylaxis of pertussis?
Macrolides (e.g., azithromycin, clarithromycin, erythromycin) can be used for the treatment of pertussis if given during the catarrhal stage. Macrolides are also used for prophylaxis in close contacts of infected patients.
What is the presentation of the catarrhal phase of B. pertussis infection?
The catarrhal phase presents similarly to a cold with mild coughing and sneezing. While the clinical course may appear mild, the patient is highly contagious during this stage.
What 2 types of media can used for Bordetella pertussis culture?
B. pertussis can be cultured on Regan Lowe or Bordet-Gengou (potato) agar.
Why is pertussis an emerging problem in the western world? What patient population is particularly susceptible?
Although pertussis is a preventable disease, infection is an emerging problem in the western world due to controversy regarding vaccination. Infection with B. pertussis should be considered in unvaccinated children and afebrile adults (> 9 years old) with a cough > 2 weeks.
What is the reservoir of B. pertussis? What is the most common mode of transmission?
Humans are the only reservoir of Bordetella pertussis. Adolescents and adults commonly transmit the pathogen via respiratory droplets to unvaccinated infants.
What B. pertussis vaccine is given to adolescents and adults?
The Tdap (Tetanus, Diphtheria, Pertussis) booster is given to adolescents and adults.
How long is the incubation period of Bordetella pertussis? What are the 3 major phases of infection?
B. pertussis has an incubation period of 2 weeks, followed by 3 major phases:
- Catarrhal
- Paroxysmal
- Convalescent
What is the morphology, gram stain, and presence of a capsule of Bordetella pertussis?
Bordetella pertussis is a gram-negative, encapsulated coccobacillus.
What is the primary treatment for pertussis in infants and children?
The primary treatment for pertussis in infants and children is supportive care.
What is the presentation of the paroxysmal phase of Bordetella pertussis infection?
The paroxysmal phase is characterized by the classic “whooping” cough of pertussis.
Do macrolides alter the disease course if given during paroxysmal phase of pertussis?
Macrolides may decrease bacterial shedding but do not alter the disease course if given during paroxysmal (severe coughing) stage.
What disease does Bordetella pertussis cause?
B. pertussis causes whooping cough, a highly contagious acute respiratory infection.
What are the 3 major toxins synthesized by B. pertussis?
In addition to LPS, B. pertussis has 3 major toxins:
- Pertussis toxin
- Adenylate cyclase toxin
- Tracheal toxin
What is the mechanism of action of the tracheal cytotoxin of B. pertussis?
Tracheal cytotoxin inhibits DNA synthesis in ciliated epithelial cells, causing cell death. Loss of ciliated epithelial cells allows debris to accumulate in the lungs, resulting in coughing fits.
What is the classic presentation of a Bordetella pertussis infection?
The classic presentation of whooping cough is an unvaccinated child that “whoops” on inspiration and coughs on expiration.
What is the presentation of the convalescent phase of Bordetella pertussis infection?
The convalescent phase is characterized by a gradual reduction in the severity and frequency of cough.
What is the mechanism of action of the two components of Pertussis toxin?
Pertussis toxin is an ADP ribosylating A-B toxin with two components:
- A (Active) component ADP-ribosylates Gi by removing the ADP-ribosyl group from NAD and covalently attaching it to Gi which causes Gi inactivation and subsequently increased cAMP, increased secretion of Na+, Cl-, H2O from cells, edema, and neutrophil dysfunction.
- B (Binding) component facilitates endocytosis.
What antibiotics are used to treat Legionnaire’s disease?
Treatment for L. pneumophila is macrolides such as azithromycin and respiratory tract fluoroquinolones such as levofloxacin.
On what media does Legionella pneumophila grow?
L. pneumophila grows on charcoal yeast extract with iron and cysteine.
Gram-negative bacilli are cultured from a 65-year-old patient with severe pneumonia and neutropenia. The hospital’s infectious disease team confirms that transmission was via aerosolized water droplets from an air conditioning unit. Which media was used to culture this organism?
A) Chocolate agar
B) Buffered charcoal yeast extract agar
C) Bordet-Gengou agar
D) MacConkey’s agar
E) Thayer-Martin agar
Buffered charcoal yeast extract agar
Answer Explanation
Aerosolized gram-negative bacilli causing severe pneumonia in an older indiivdual suggests Legionnaire’s disease. This fastidious organism grows on charcoal yeast extract agar, usually requiring increased iron and cysteine levels.
MacConkey’s agar can be used to identify lactose fermenters (pink colonies).
Thayer-Martin agar is used to culture Neisseria gonorrhoeae.
Bordet-Gengou agar is used to culture Bordatella pertussis.
Chocolate agar is often used to culture Haemophilus influenzae.
What is the difference between Legionnaire’s disease and Pontiac fever?
L. pneumophila causes severe, atypical pneumonia termed Legionnaire’s disease or self-limiting Pontiac fever that presents with a mild flu-like illness (fever, chills, fatigue, malaise, and headache) without respiratory symptoms.
What stain is most useful for visualizing Legionella pneumophila?
L. pneumophila gram stains weakly, but silver stain can be used.
How is Legionella pneumophila diagnosed?
Diagnosis of L. pneumophila infection is made via the presence of antigen in urine.
What is the gram stain, morphology, and oxidase status of Legionella pneumophila?
Legionella pneumophila is a facultative intracellular, oxidase-positive, gram-negative bacillus.
What stain should be used to detect Legionella?
A) AFB
B) Gram stain
C) PAS
D) Silver stain
E) India ink
Silver stain
Answer Explanation
Unlike the majority of high-yield bacteria, Legionella is poorly visualized with Gram staining. Instead, silver staining should be used to detect the presence of Legionella.
What is the abnormal electrolyte level in Legionella pneumophila infections?
Hyponatremia is an important, distinguishing feature of Legionella pneumonia. This may be related to inappropriate ADH secretion and/or renal tubulointerstitial disease impairing sodium reabsorption.
How is Legionella pneumophila transmitted? What are examples of sources for Legionella pneumophila?
Transmission of L. pneumophila occurs via aerosols from environmental water sources such as air conditioning systems and hot water tanks.
