Respiratory Infections Flashcards
Legionella Pneumonia
Gram negative rod (often not detected on gram stain)
Legionnaires’ disease; most common cause of communicy acquired pneumonia; contaminates water, spread by inhalation of aerosolized water from natural water sources, tap water in healthcare facilities, air conditioners, other water based cooling systems
symptoms: very high fever 104ºF, 40ºC history of smoking diarrhea confusion cough (initially only slightly productive) Labs show hyponatremia
diagnosis difficult because of non-specific symptoms.
look for radiographic evidence of pneumonia, high fever, accompanying GI symptoms (diarrhea)
sputum sample unreliable, SHOWS FEW OR NO BACTERIA since unique lipopolysaccharide chains on outer membrane inhibit gram staining.
diagnosis made by testing legionella antigen in urine
Tx:
fluoroquinolones (levofloxacin) or newer macrolides (azithromycin)
Ddx:
mycobacterium Kansasii atypical mycobacterium that can casue similar to M. tuberculosis (acid fast rod similar to L. Pneumonphila in that it’s water contaminant) but it’s usually municipal drinking water systems not nature.
Mycoplasma Pneumoniae
Primary cause of walking pneumonia
symptoms: nagging nonproductive cough, low grade fever, malaise
CXR suggests severe pneumonia even though patient appears relatively well
Mycoplasma species require cholesterol supplementation to grow on artificial media (lack a peptidoglycan cell wall, cell envelope or capsule
Ddx:
strep pneumoniae causes lobar consolidation on CXR, grows on unenriched blood agar, unable to grow in optochin or bile
Kleb Pneumoniae common in debilitated, hospitalized or alcoholics (red currant jelly sputum), grows on any agar but MacConkey agar is best bcz contains bile which inhibits growth of contaminant organism
H. Influenzae requires chocolate agar (heat lyzed blood agar) supplemented with facor X (hematin) and factor V (NAD+) in order to grow
L. pneumophila requires L-cysteine - supplemented agar for growth
Coxiella burnetii causes Q-fever (mild pneumonia-like illness resulting from inhalation of C. Burnetti spores in animal hides.) obligate intracellular parasite needs CELL CULTURE in order to grow
Fungi (coccidioides immitis - san joaquin valley fever) common in southwest US and northern Mexico. Histoplasma capsulatum causes similar illness but typically in Mississippi and Ohio river valleys. both can be cultured on standard bacterial culture media.
Pneumocystis jiroveci is a fungus that cuases severe Pneumonia in HIV+ patients whose CD4 is below 200. ground glass CXR. pneumocytstic jiroveci (PCP) by silver stain during bronchoscopy.
Fungi require ergosterol for growth (drug target)
Asplenic patients prone to infections by
Post-splenectomy infection carries 50% mortality risk
spleen is part of lymphoid system. destruction of RBC, serves are reservoir of RBC, granulocytes and platelets that can be mobilized when needed. Macrophages that line the trabecular meshwork present antigens to B and T cells in splenic white pulp to generate active immune response.
Asplenic patients are prone to infections by encapsulated organisms like S. pneumoniae, H. influenzae, N. meningitidis
spleen serves as site of Ab synthesis and reservoir of phaogyctic cells capable of removing circulating pathogens.
Interstitial Pneumonia with oral thrush and severe lymphopenia during first year of life in baby born to IV drug user indicates what infection? what’s the preventative protocol?
HIV infection. maternal prophylaxis during pregnancy with nucleoside analog zidovudine (ZDV/AZT) - retroviral reverse transcriptase inhibitor, reduces the risk of perinatal transmission by 2/3 in HIV positive women who have not previously received antiretroviral therapy.
immune cells that fight Tuberculosis
Pulmonary tuberculosis infection is controlled by the action of CD4+ TH1 llymphocytes and macrophages. These cells work together to contain M. Tubercuolsis within a caseous granuloma, which offers the macrophages inside an opportunity to kil the remaining organisms if the necrotic area is small enough.
Haemophilus Influenzae growth (satellite phenomenon)
Haemophilus species are part of normal flora of Upper resp tract, must differentiate it forom other bacteria through biochemical means. Demonstrate it by showing necessity of X and V factors.
blood loving organism. need factor X(hematin) and V (NAD+) for growth. grow on chocolate agar plate, or around streak of staph aureus due to NAD+.
grow near beta hemolytic S. aureus colonies because they produce factors X and V.
Staph is ß-hemolytic, X factor released and V factor actively secreted by staphylococci into growth medium. both X and V needed by H. influenzae.
Mycoplasma pneumoniae and anemia
mycoplasma pneumoniae is causative agent of walking pneumonia and many cases of tracheobronchitis. has no peptidoglycan cell wall. Only has a phospholipid bilayer cell membrane. Shares antigens with human erythrocytes, and when the body mounts a response against these antigens it also lysis red blood cells leading to anemia. the antibodies causing this RBC destruction are called cold agglutinins becuase they are able to agglutinate RBCs in vitro at low temperatures.
M. pneumoniae can also cause stevens-johnson syndroma nd joint pains among other rare sequelae.
Histoplasma Capsulatum
can survive intracellular within macrophages. It causes a disseminated mycosis in immunocompromized patients. The clinical features include systemic symptoms (fever and weight loss) fiainful oral ulcers, lymphadenopathy, hepatosplenomegaly.
Hyper IgM syndrome
results from inability of B-lymphocytes to undergo isotype switching from IgM to other immunoglobulin isotypes like IgD, IgG, IgE and IgA. Clinically, hyper-IgM syndrome most commonly restuls in lymphoid hyperplasia and recurrent sinopulmonary infectinos. The syndrome results most commonly from a genetic absence of the CD-40 ligand on T-lymphocytes or from a genetic deficiency in the enzymes responsible for the DNA modification that takes place during istoype switching.
Group A strep - S. pyogenes
ß hemolytic, bacitracin sensitive
Group B strep - S. agalactiae in newborns
ß-hemolytic gram positive cocci in chains - bacitraicn resistant
screen prenatally for vaginal and rectal culture at 35-37 weeks gestation. Positive cultures or previous positives, intrapartum antibiotic prophylaxis indicated to prevent neonatal GBS sepsis, pneumonia and meningitis.
Echovirus (picornaviridae family)
single stranded, positive-sense, linear, nonsegmented RNA virus have genome that is independentely active, works as its own mRNA, produces polypeptide coding for several proteins and then cleaves the protein products.
viruses with single-stranded, negative sense, linear RNA
nonsegmented (measles and rabies)
segmented (influenza virus)
S. Pneumoniae polysaccharide vaccine
lancet shaped gram positive diplococci.
80 serotypes with variants of capsular polysaccharide.
types 1-8 repsonsible for 75% of dinfections.
23-valent pneumococcal polysaccharide single dose vaccine is recommended for all adults over age 65 and other patients at high risk of pneumococcal sepsis (HIV, asplenia, COPD, immunosuppressed). 50-90% efficacy.
7-valent conjugated vaccine for kids under 2yo, 90% efficacy.
conjugated vaccine contains polysaccharide antigens that are protein coupled to stimulate the T-cell dependent immune (memory) response.
also vaccine for N. Meningitidis and H. Influenze that are also polysaccharid vaccines.
Aspergillus fumigatus
low virulence fungus does not cause significant infections except in immunocompromized or debilitated patients. Can complicate asthma or CF via a hypersentivity reaction. result is allergic bronchopulmonary aspergillosis or ABPA.
occurs in 5-10% of steroid dependent asthmaics. high serum IgE levels, eosinophilia and IgE plus IgG serum antibodies to Asdpergillus.
causes allergic bronchopulmonary aspergillosis (ABPA) due to aspergillus fumigatus can complicate asthma. ABPA can result in transient recurrent pulmonary infilatrates and eventual proximal bronchiectasis.
Pseudomonas aeruginosa
opportunistic aerobic gram-negative rod that is frequent, sometimes deadly, pulmonary pathogen in patients with CF or neutropenia.
Strongyloidiasis
can cuase pulmonary sympotms: cough, asthma like bronchospasm and hemoptysis. can also produce a transient pneumonia as larvae migrate through the lungs on their way ot the laryngopharynx. In rare cases, chronic lung involvmenet may cause features of obstructive and/or restirctive pulmonary disease.
Legionella pneumophila
commonly contaminates natural bodies of water, municipal water, humidification systems and air conditionsing and water based cooling systems. inhaled in aerosolized water and establishes infection by the pulmmonary route. requires special enrigched media for growth (L-cysteine) and agar used is buffered charcoal yeast extract agar.
