Bacterial Pneumonia 2- Atypical Pneumonias Flashcards
What is the bacteriology of Legionella?
- gram neg rods
- stains poorly by gram or H&E; requires silver or IF in tissue sections
- facultative intracellular parasites
- free living form is motile (flagella); intracellular form is non-motile
What the reservoirs for legionella?
- Natural- intracellular parasites of freshwater protozoa
- unnatural- biofilms in commercial water systems, aspirated by humans
How does Legionella replicate?
- it begins living in a biofilm on warm water or in soil
- it is taken up by phagocytosis
- contained in an altered phagosome- NOT merged to a lysosome
- it becomes motile and escapes the phagosome
- lyses the cell and spreads to another
- humans are an unnatural dead end host for legionella- eventually it runs out of alveolar macrophages to infect, can’t spread person to person
What are the virulence factors of legionella?
- mip= unknown, required to invade monocytes
- Dot/Icm locus- type IV secretion system (involved in altering the endosome)
- pilE and pilD- pilus formation (attachment)
- Mak- unknown
- Mil- unknown
- pmi- unknown
- Pep/pro- zinc metalloprotease (escape)
What are the possible outcomes of a legionella infection?
- asympomatic seroconversion
- pontiac fever
- Legionnaires Disease
- all three outcomes are causes by the same organism- one outbreak may generate all three patient types, differences are in the hosts possibly also dosage
What is pontiac fever?
- infection with Legionella
- flulike
- incubates hours- 2 days
- resolves without complication
What is Legionnaires Disease?
- infection with Legionella
- pneumonia
- suppression of kidney function
- incubates 2-10 days
- usually resolves with hospitalization and treatment
- can be fatal
What are risk factors for Legionnaires Disease?
- increasing age
- immunosuppression
- smoking
- chronic heart or lung disease
- chronic swallowing disorder
- male
- for outbreak LD, travel is a common factor: conventions and weddings at hotels
What is the occurrence and mortality of Legionnaires Disease?
- 80% cases are isolated, 20% outbreak
- reportable
- outbreaks are a simultaneously-exposed group: NOT contagious
- 8000-18000 hospitalizations/year in US; 2nd most common pneumonia ICU admit (after pneumococcal)
- 34% mortality in US in 1985, 11.5% in 1998
- mortality decreasing because of: prompt diagnosis, early use of appropriate antibiotics
Why are there Nosocomial Legionnaires Disease Outbreaks?
- hospitals are hot spots for LD outbreaks
- large numbers of at risk individuals
- old, complex plumbing
- hot water tanks at reduced temperature to prevent scalding (Fix: thermal mixing valves)
How does Legionnaires Disease present?
- high fever/chills
- pneumonia/cough/chest pain
- pancreatitis
- diarrhea*
- acute renal failure
- headache
- altered mental status
- not clinically distinct from other pneumonias. Need lab results to differentiate
How do you diagnose Legionella Infection?
-Urine antigen test: Commercial ELISA kit, fast: cell wall component is excreted starting 3 days after symptom onset and test complete in hours; reliably detects the LP1 strain of L pneumophilia (causes 90% of LD in US); testing significantly associated with reduced mortality
Culture of Respiratory Secretions- much slower (1 wk), technically demanding, detects many strains and species of Legionella, 27% fatality rate among culture positive, urine-test negative patients, grow on Buffered Charcoal Yeast Extract with alpha-keto-glutarate
How are Legionella infections treated?
- Pontiac Fever often resolves without treatment, could put on cipro if concerned about Legionnaires
- LD requires an antibiotics that penetrates infected cells: Levofloxacin (also covers M pneumoniae and S pneumoniae); Azithromycin, erythromycin (old school)
- post acute care: they experience fatigue, neurological symptoms, neuromuscular symptoms, cough for up to 17 months most recover completely within one year
What is the bacteriology of Coxiella burnetii (Q fever)
- previously grouped with Rickettsia, now a Proteobacteria (closest related pathogen: Legionella)
- zoonosis of asymptomatic infection of ruminants
- transmitted to humans by inhalation of aerosols of infected ruminant urine, feces, birthing matter (no vector)
- extremely infectious: <10 IUs can cause disease, dried samples remain infectious for months
How do humans become infected with C burnetii?
- in humans it multiples within alveolar monocytes and macrophages (after being breathed in), travels in them to liver, spleen, bone marrow
- fairly common in Netherlands, France, Spain and becoming a problem among military and medical personnel in Iraq
What are the virulence factors of C burnetii?
- acid phosphatase
- superoxide dismutases- help bacteria survive in FUSED lysosome-endosome
How does a C. burnetti infection present?
- fever, chills, sweats
- severe headache
- dry cough
- pneumonia*
- hepatitis*
- complications of pregnancy
- rare: rash, endocarditis
- rarely fatal
- reportable
How do you diagnose and treat a C. burnetti infection?
- same as Rickettsia: immunohistochemical methods, ELISA, immunofluorescence
- doxycycline or fluoroquinolones
- prevention: vaccine is available to farm and veterinary personnel and military stationed in Middle East
What is the bacteriology of Mycoplasma
- smallest freeliving organisms (0.3 micrometer diameter)
- strictly aerobic
- no cell wall: little gram staining, penicillins and cephalosporins therefore ineffective
- only prokaryotic cell membrane that contains cholesterol
- difficult to grow on media, require special nutrients
- colonies have a fried egg shape
- only one serotype, but immunity is incomplete
What is the pathogenesis of Mycoplasma?
- reside on mucosal surfaces of respiratory and genital tracts
- transmitted by inhalation of respiratory aerosols
- causes tracheobronchitis, bronchiolitis, 5-10% progress to atypical walking pneumonia
- P1 adhesion binds respiratory epithelial cells
- Ciliostasis- dry cough, exacerbates chronic bronchitis, asthma
- local inflammation from bacterial wastes
- tissue destruction by CARDS exotoxin (related to pertussis toxin)
- intracellular penetration possible
- causes 20% of community acquired pneumonias that require admission
- VERY low mortality <0.1%
- antibiotics against mycoplasma (cold agglutinins) cross react with RBC membranes so patients may become anemic
How is Mycoplasma diagnosed?
- exam: nonspecific upper and lower airway, fever, aches and pains, oropharyngeal inflammation, erythematous tympanic membranes, conjunctivitis, rash, lung sounds may include moderate rhonchi and rales
- chest radiograph often looks worse than the patient
- labs: self limited and antibiotic responsive, not usually culture and molecular available. May be anemic
How do you treat Mycoplasma?
- Fluoroquinolones cover mycoplasma and all similarly-presenting bacterial infections
- erythromycin, azirthomycin, clarithromycin, tetracycline all work slightly better against mycoplasma
- longer treatment courses (14-21d) needed because of M’s slow growth, intracellular penetration
- macrolide resistance is emerging in Japan and China
What are some other Mycoplasma?
- ureaplasma urealyticum and U. parvus can cause male urethritis, possibly also premature birth
- M genitalium can contribute to male urethritis, female cervicitis and PID
- ureaplasma and mycoplasma may both cause bacteremic pneumonia in very premature infants
- all can be passed by direct contact, vertically, or nosocomial
