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
