Respiratory Pathogens

Question 1

Rhinovirus

Answer 1

Most common cause of the common cold. Transmitted by hand to eye-nose contact. Other causes of colds: coronaviruses, adenoviruses, influenza C virus, coxsackievirus

Question 2

Coxsackievirus

Answer 2

Acute chest syndrome; fever with pleuritis

Question 3

Parainfluenza

Answer 3

Most common cause of croup (laryngotracheobronchitis) in infants. Inspiratory stridor (upper airway obstruction) due to submucosal edema in trachea; brassy cough; signs of respiratory distress. Anterior x-ray of neck shows “steeple sign,” representing mucosal edema in the trachea (site of obstruction). Bronchiolitis in infants. Treatment: cold water humidifiers and aerosolized racemic epinephrine.

Question 4

CMV

Answer 4

Common pneumonia in immunocompromised hosts (bone marrow transplants, AIDS). Enlarged alveolar macrophages/pneumocytes, contain eosinophilic intranuclear inclusions surrounded by a halo. Treatment: cidofovir, foscarnet, ganciclovir.

Question 5

Influenzavirus

Answer 5

Type A viruses most often involved. Hemagglutinins bind virus to cell receptors in nasal passages. Neuraminidase dissolves mucus and facilitates release of viral particles. Influenza A: worldwide epidemics; pneumonia may be complicated by a superimposed bacterial pneumonia (usually Staphylococcus aureus). Influenza B causes major outbreaks. Antigen drift: minor mutation; does not require new vaccine. Antigen shift: major mutation in hemagglutinin or neuraminidase; new vaccine required. Clinical: fever, headache, cough, myalgias, chest pain. Vaccination: mandatory for people >65 years old, people with chronic illnesses. Treatment: neuraminidase inhibitors (oseltamivir). Associations: Reye syndrome with salicylate ingestion; Guillan-Barre syndrome.

Question 6

Rubeola

Answer 6

Fever, cough, conjunctivitis and excessive nasal mucus production. Koplik spots in mouth precede rash onset. Warthin-Finkeldey multinucleated giant cells.

Question 7

Respiratory syncytial virus (RSV)

Answer 7

Most common cause of pneumonia and bronchiolitis (wheezing) in infants. Causes otitis media in older children. Hand washing and use of gloves prevents nosocomial outbreaks in nurseries. Fusion protein causes cells to fuse, producing multinucleated giant cells. Infections primarily occur in winter. Rapid diagnosis by detection of antigen in nasopharyngeal wash. Passive immunization (high risk kids): palivizumab (monoclonal antibody) reduces hospitalization rates between November and April.

Question 8

SARS

Answer 8

First transmitted to human through contact with masked palm civets (China) and then from human-to-human contact through respiratory secretions (hospitals, families). Develop severe respiratory infection. Diagnose with viral detection by PCR assay or detection of antibodies. Children: no therapy or vitamin A.

Question 9

Hantavirus pulmonary syndrome

Answer 9

Transmission: inhalation of urine/feces from deer mice in Southwestern United States. Pulmonary syndrome: ARDS, hemorrhage, renal failure. Diagnosis: detect viral RNA in lung tissue. No effective treatment. High mortality rate.

Question 10

Chlamydophila pneumoniae

Answer 10

Second most common cause of atypical pneumonia. Seroepidemiologic association with coronary artery disease. Treatment: doxycycline.

Question 11

Chlamydia trachomatis

Answer 11

Newborn pneumonia (passage through birth canal). Afebrile, staccato cough (choppy cough), conjunctivitis, wheezing. Treatment: erythromycin.

Question 12

Mycoplasma M. pneumoniae

Answer 12

Most common cause of atypical pneumonia. Common in adolescents and military recruits (closed spaces). Risk factor for Guillan-Barre syndrome. Insidious onset with low-grade fever. Cold agglutinins in blood. Complications: bullous myringitis, cold autoimmune hemolytic anemia due to anti-I IgM antibodies. Treatment: erythromycin; azithromycin; clarithromycin.

Question 13

Coxiella burnetii

Answer 13

Usually transmitted without a vector. Contracted by dairy farmers, veterinarians. Associated with birthing process of infected sheep, cattle and goats, and handling of milk or excrement. Atypical pneumonia, myocarditis, granulomatous hepatitis. Treatment: doxycycline.

Question 14

Streptococcus pneumoniae

Answer 14

Gram-positive lancet-shaped diplococcus. Most common cause of typical community-acquired pneumonia. Rapid onset, productive cough, signs of consolidation. Urine antigen test excellent screen. Treatment: penicillin G (penicillin sensitive); vancomycin +/- rifampin (penicillin resistant).

Question 15

Staphylococcus aureus

Answer 15

Gra-positive cocci in clumps. Yellow sputum. Commonly superimposed on influenza pneumonia and measles pneumonia. Major lung pathogen in cystic fibrosis and IV drug abusers. Hemorrhagic pulmonary edema, abscess formation, and pneumatoceles (thin-walled air-filled cysts that develop in the lung parenchyma, usually after pneumonia). Treatment of pneumonia: methicillin-sensitive: nafcillin or oxacillin; methicillin resistant: vancomycin.

Question 16

Corynebacterium diphtheriae

Answer 16

Gram-positive rod. Toxin inhibits protein synthesis by ADP-ribosylation of elongation factor 2 involved in protein synthesis. Toxin also impairs beta-oxidation of fatty acids in heart. Toxin-induced pseudomembranous inflammation produces shaggy gray membranes in oropharynx and trachea; toxic myocarditis (death). Treatment: erythromycin.

Question 17

Bacillus anthracis

Answer 17

Gram-positive rod. Habitat: soil. Capsule inhibits phagocytosis. Exotoxins: edema factor (activates adenylate cyclase); lethal factor (inhibits a signal transduction protein involved in cell division); protective antigen (assists entry of above toxins into cells). Transmission: direct contact with animal skins or products (most commonly sheep and cattle) and entry of the organisms through abrasions or cuts; inhalation (use in germ warfare). Cutaneous anthrax (90-95% of cases): occurs through direct contact with infected or contaminated animal products; resembles insect bite but eventually swells to form black scab (eschar) with central area of necrosis (malignant pustule); if untreated, death occurs in 20% of patients. Pulmonary anthrax: first sign of disease is death; inhalation of spores present in contaminated hides or biological weapon; necrotizing pneumonia, meningitis, pronounced splenomegaly, and dissemination throughout the rest of body. Prevention: vaccine available for high-risk patients; veterinarians, soldiers entering developing countries. Treatment: ciprofloxacin.

Question 18

Actinomyces israelii

Answer 18

Gram-positive filamentous bacteria; strict anaerobe; normal flora in tonsils and adenoids. Produces draining sinuses in jaw, chest cavity, and abdomen; pus contains sulfur granules (yellow specks) that contain the bacteria. Treatment: ampicillin or penicillin G.

Question 19

Nocardia asteroides

Answer 19

Gram-positive filamentous bacteria; strict aerobe; partially acid-fast. Produces granulomatous microabscesses in lungs. Frequently disseminates to CNS and kidneys. Treatment: TMP-SMX.

Question 20

Bordetella pertussis

Answer 20

Gram-negative rod. Pili attach to cilia in upper respiratory tract; toxin stimulates adenylate cyclase, which catalyzes addition of ADP-ribose to the inhibitory subunit of the G protein complex; toxin also produces absolute lymphocytosis (normal-appearing lymphocytes) often in leukemoid reaction range. Produces whooping cough, transmitted by droplets. Catarrhal phase: lasts 1-2 weeks; mild coughing; rhinorrhea, conjunctivitis. Paroxysmal coughing phase: lasts 2-5 weeks; characteristic 4-5 coughs in succession on expiration followed by an inspiratory whoop; absolute lymphocytosis (20,000-50,000cells/mm^3). Convalescence phase: lasts 1-2 weeks; slow decline in coughing and lymphocytosis. Complications: hemorrhage into skin, conjunctiva, bronchus, brain from coughing; otitis media; meningoencephalitis (10%); rectal prolapse from coughing; pneumonia (most common cause of death in children <3 years old; children <1 year old have no protection from mother’s immunoglobulins). Diagnosis: nasopharyngeal swabs using special cough plate; direct immunofluorescence of swab material. Treatment: erythromycin.

Question 21

Haemophilus influenza

Answer 21

Gram-negative rod
Common cause of sinusitis, otitis media, conjunctivitis (pink eye). Inspiratory stridor may be due to acute epiglottitis. Swelling of epiglottis produces “thumbprint sign” on lateral x-ray of neck. Most common bacterial cause of acute exacerbation of COPD. Treatment: cefotaxime; ceftriaxone.

Question 22

Moraxella catarrhalis

Answer 22

Gram-negative diplococcus. Common cause of typical pneumonia, especially in elderly. Second most common pathogen causing acute exacerbation of COPD. Common cause of chronic bronchitis, sinusitis, otitis media. Treatment: amoxicillin-clavulanate.

Question 23

Pseudomonas aeruginosa

Answer 23

Green sputum (pyocyanin)
Water-loving bacteria most often transmitted by respirators. Most common cause of nosocomial pneumonia and death due to pneumonia in cystic fibrosis. Pneumonia often associated with infarction due to vessel invasion. Treatment: antipseudomonal beta-lactam + aminoglycoside + antipseudomonal quinolone or macrolide.

Question 24

Klebsiella pneumoniae

Answer 24

Gram-negative fat rod surrounded by a mucoid capsule. Common gram-negative organism causing lobar pneumonia and typical pneumonia in elderly patients in nursing homes. Common cause of pneumonia in alcoholics; however, S. pneumoniae is still the most common pneumonia. Typical pneumonia associated with blood-tinged, thick mucoid sputum. Lobar consolidation and abscess formation are common. Treatment: varies with susceptibility.

Question 25

Legionella pneumophila

Answer 25

Gram-negative rod (requires IF stain or Dieterle silver stain to identify in tissue). Antigens can also be detected in urine. Water-loving bacterium (water coolers; mists in produce section of grocery stores; outdoor restaurants in summer; rain forests in zoos). Risk factors: alcoholic, smoker, immunosuppression. Atypical pneumonia associated with high fever, dry cough, flu-like symptoms. May produce tubulointerstitial disease with destruction of the JG apparatus leading to hyporeninemic hypoaldosteronism (type IV renal tubular acidosis -hyponatremia, hyperkalemia, metabolic acidosis). Urine antigen test excellent screen. Treatment: fluoroquinolone; azithromycin.

Question 26

Yersinia pestis

Answer 26

Gram-negative rod
Cause of plague
Transmitted by bite of rat flea; primary reservoir for bacteria are ground squirrels in Southwest. Also transmitted person-to-person by droplet infection. Macrophages cannot kill bacteria because V and W antigens provide protection. Three types of disease: bubonic (most common), pneumonic (transmitted by aerosol), septicemic. Bubonic type: bite by rat flea that has recently bitten an infected ground squirrel; infected lymph nodes enlarge (usually in the groin), mat together and drain to surface (buboes). Treatment: pneumonic type: gentamicin.