Pneumonia can be from either infection or INFLAMMATION of the lung, and inflammation can occur due to aspiration of gastric acid, inhalation of smoke or other noxious chemicals, burns, etc. Some texts use pneumonitis for inflam that is restricted to interstitial tissue (not including alveoli)
What's the most common way that people get pneumonia?
by inhaling droplets of saliva
How else can you get it?
hematogenous or lymphatic spread of the infectious agent, or invasion of the infection from adjacent tissue
How many Americans get pneumonia each year?
How many die of it in a year?
--most common nocosomial infx in US
--6th leading cause of death in US
--2nd leading cause of death in 3rd world, diarrhea is 1st
What are the risk factors for developing pneumonia?
--being old and frail
--decreased cough response and gag reflex (esp inhaling vomitus)
--any state of impaired consciousness (esp alcoholism)
--having been intubated or on a ventilator
--smoking tobacco or inhaled chemicals (dt impaired cilia fx)
--poor dental hygiene & oral dz
--pulmonary edema esp chronic
--lowered resistance (lowered white count or complement defects)
What are the typical symptoms of pneumonia?
--cough, fever, fatigue, myalgias, increased sputum production
--shortness of breath
--pleuritic chest pain, knifelike, throbbing
--URI sx incl: sore throat, nasal congestion, post nasal drip, sinus congestion
--sputum may turn "rust" colored dt RBC's & WBC's
--severe pneumo may present w/o cough or fever
What are the usual physical exam findings for pneumo?
--fever, tachycardia, tachypnea
--cracks on auscultation or absence of sound indicating consolidation
--dullness of lung fields to percussion
--these findings more common with bacterial infx such as Strep pneumo (lobar)
--bacterial more likely to cause consolidation
What's the difference between lobar and lobular pneumonia?
The distinction is generally made by chest x-ray.
A person's history and presentation may be consistent with pneumonia and yet the x-ray is negative.
Lobular is characterized by patchy consolidation caused by viruses and specific bacteria, and is also known as bronchopneumonia.
Lobar pneumonia shows consolidation of a particular lobe or lobes, while other lobes are uninfected.
What are the four stages of lobar pneumonia? (useless clinically but sure to be on boards)
1) congestion = vascular engorgements and development of intra-alveolar fluid with few neuts and many bact
2) red hepatization = exudate of RBC's and neuts and fibrin fills alveoli, looks red, firm, airless (like liver)
3) grey heptization = red cells disintegrate and fibrinous suppurative exudate persists, giving gray-brown superficial appearance, drier than previous stage
4) resolution = consolidated exudate undergoes progressive enzymatic digestions to produce semifluid debris that is resorbed or coughed up (1-3 months, lungs may be scarred)
What are the commonest bacteria that cause community acquired pneumonia:
1) Streptococcus pneumoniae = most common acute
2) Haemophilus influenza
3) Moraxella catarrhalis
(previous three like to live in sinuses too)
4) Staphylococcus aureus
5) Legionella pneumophila => atypical, from aerosolized h2o inhalation
6) Klebsiella pnuemoniae (gram -)
Name the top causes of atypical community aquired pneumonia.
1) Mycoplasma pneumoniae = #1, same bug that causes bullous myringitis in ear
2) Chlamydia spp. (C. pneumoniae, C. psittaci, C. trachomatis)
3) Coxiella burnetti (Q fever)
4) VIRUSES: RSV (respiratory syncitial virus is most common culturable virus), parainfluenza virus, Varicella, influenza A & B, adenovirus, SARS (a coronavirus)
What group of agents most commonly cause early childhood pneumo?
What telltale histological feature do HSV and RSV have in common?
multinuclear giant cells
Which viruses are most likely to cause pneumonia in adults?
influenza A or Varicella-zoster
What are the top causes of NOSOCOMIAL pneumonias?
1) gram - rods suchs as Kelbsiella, Pseudomonas and E. coli
2) Staph aureaus (often penicillin resistant)
Which aerobic bacteria are likely to be mixed with anaerobic oral flora (Bacteroides, Fusobacterium) to cause aspiration pneumonia?
1) Strep pneumo
2) Staph aureus
3) H. flu
What additional organisms cause pneumonia in an immunocompromised host?
--fungi incl: aspergillus and candida
What is the most common cause of pneumonia in HIV/AIDS patients?
--also affects pts undergoing chemo, or on immunosuppressants esp after transplant of bone marrow
--causes high fever, dry cough an marked dyspnea
--marked red hepatization phase
--use silver stain to ID from sputum or biopsy
--pts with CD4 counts below 200 usu on prophylactic abx (trimethoprim sulfa or pentamadine)
What fungal infection shows onionskin lamellar lesions in lung tissue?
--clinically resembles viral infx
--chronic infx results in cavitary dz in upper lobes or granulomas that resemble TB
What fungal infection is commonly acquired in the desert SW?
--80% of indigenous pop shows skin rxn to antigen
--plural effusions common in pts with this pneumo
--dry cough and high fever
--histol: thick-walled non-budding spherules filled with endospore
What common mold can invade opportunistically and form abscesses in lungs?
--layered hyphae are diagnostic
What is the single most infectious cause of death on earth?
tuberculosis (Mycobacterium tuberculosis and M bovis)
--infects 1/3 of the world's pop
--kills ~3 million/year
--Dx from histol w/ AF stain: waxy coated linear bugs that fold, "red snappers"
--immunocompromise--> also look out for M. avium, M. intracellulare
--after alveolar macrophages engulf inhaled mycobacterium they transport to hilar lymph nodes where they multiply, CD4 cells secrete interferon-->NO in macrophages to kill invader, CD8 cells also lyse infected macrophages contributing to granulomas with central necrosis--> characteristic caseous granulomas
--drug resistance increasing
--can cause severe bronchopneumonia (lobular)