Atypical pneumonia Flashcards
Compare the differing clinical presentations of typical and atypical pneumonia?
o Typical- lobar, mucopurulent sputum, acute 1-2days, lobar pneumonia (confined to 1 lobe)
o Atypical- bilateral crackles in all lung zones, “walking pneumonia”, scant/watery sputum, low-grade fever, longer presentation 10days, interstitial infiltrates, patchy consolidation
List some DDx for a presentation of:
- low grade fever
- non-productive cough
- malaise, lethargy
- bilat crackles
- lower lobe consolidation
• Pneumonia - atypical (mycoplasma pneumoniae, chladmydia pneumoniae) - typical (Step pneumoniae, H influenzae) - viral (influenza A or B) - fungal (aspergillus, cryptococcus spp) • LRTI - bronchitis - bronchiectasis - TB - COPD, asthma infective exacerbation • URTI - sinusitis - pharyngitis • Cardiac- CCF exacerbation • Malignancy- lung ca, mets
Describe the possible causative organisms:
CAP
• Typical:
o Step pneumoniae (60%)- GN diplococci
o H influenzae (15%)- GN coccobacilli
• Atypical: (organisms not visible on gram stain, not culturable on standard blood agar)
o Mycoplasma pneumoniae – nil GN reaction (nil cell wall), attaches to resp ciliated epithelium
- Clinical: persistant cough, can exacerbate asthma, esp young adults
o Chlamydia pnaeumoniae- obligate intracellular, GN -> inhibits ciliary action, grows in cells (e.g. macrophages, SM, endothelial cells)
- Clinical: persistent cough, asthma exacerbation
• Viruses: RSV, parainfluenza (children), influenza A and B, adenovirus
HAP
• Enterobacteria (GN rod)- Klebsiella pneumonia, E coli, Pseudomonas aeruginosa
• S aureus (GP cocci)- MRSA
What investigations would you do for pneumonia?
- Primary survey (ABCDE)- esp O2 sat
- CXR- gold standard
- Sputum MCS
- Blood cultures
- ABG- hypoxia, resp failure, acidosis
- FBC- leukocytosis (neutrophilia- bacterial pneumonia)
- EUC- severity scoring, Abx baseline
- LFTs- Legionella, M pneumoniae
- Procalcitonin- raised in bacterial, aids abx duration decision,
What special investigations might you do for atypical pneumoniae?
- Urinary antigen testing- pneumococcal, legionella
- Nucleic acid amplification testing (NAAT) (nose and throat swabs)- PCR influenzae, C pneumoniae, Mycoplasma, Legionella
- IgM and IgG serology- Mycoplasma pneumoniae
How would you test for mycoplasma?
- PCR nasopharyngeal swab- diagnostic choice, rapid, high specificity
- Serology- gold standard for serology diagnosis = x4 increase antibody titres over time, done with PCR or when PCR not available
NOT culture (no cell wall -> no gram stain)
How do you take a sputum culture?
• Collection- prior to Abx treatment (otherwise sensitivity decreased)
• Pt rinse mouth with saline, deep cough, plegm expectorated in sterile cup, labelled and sent for culture
• Cultures performed rapidly post collection (<2hrs)
• Smeared on agar, incubated, sensitivity checked
• Good sample: polymorphonuclear leukocytes (PMNs), but few squamous epithelial cells (SECs) on gram stain
• Interpretation:
➢ Quantity of growth- moderate/heavy for true pathogen
➢ Clinical correlation
➢ Gram stain correlation
How do you take a blood culture?
• Collection- prior to Abx treatment (otherwise sensitivity decreased)
• > 2 sites, different points in time, prior to Abx
• Culture both aerobic (first) and anerobic bottles
• Placed in blood culture machine -> incubates at body temp for 5 days
• Fluorescent disc at bottom of bottle changes colour when sufficient growth
• Positive culture -> then gram stained, agar growth and sensitivity (3 days)
➢ Sensitivity (>6mm susceptible, >2mm for vancomycin)
Describe the MA and SE of Amoxicillin?
Amoxicillin
• Class: extended spectrum penicillin
• MA: Bacteriocidal: beta-lactam ring selectively and irreversibly binds to penicillin binding proteins (PBPs) -> PBPs cannot catalyse cross-linking of peptidoglycan polymers to form cell wall -> accumulation of cell wall precursors -> activates autolytic enzyme -> cell lysis/death
• Spectrum: gram positive (cocci but not staph, and rods) and gram negative
o B-lactamase sensitive
o Mnemonic (HELPS kill enterococci): H influenzae, E coli, Listeria monocytogenes, Proteus Mirabalis, Salmonella, Enterococci
• SE: N/V (kills endogenous flora), diarrhoea, C diff, hypersensivity, photosensitivity, interstitial nephritis, encephalopathy, haematological toxicity
• Interactions: anticoags, allopurinol, some Abx
Describe the MA and SE of Macrolides? Give examples.
Macrolides
E.g. Erythromycin, Clarithromycin, Azithromycin
• MA: Bacteriostatic: binds to 50S ribosomal subunit -> prevents transfer of peptidyl tRNA after peptide bond formation -> inhibits translation -> inhibits protein synthesis
• Spectrum: broad spectrum -> GP (cocci and anaerobes), GN (cocci and anaerobes), atypicals (chlamydia, mycoplasma, legionella)
• SE (MACRO mnemonic): motility issues, arrhythmia, cholestatic hepatitis, rashes, eosinophilia
• Interactions (CYP34A enzyme): statins, CCBs, carbamazepine, oral anticoags
Describe the MA and SE of tetracylcines?
Tetracyclines
E.g. Doxycycline
• MA: Bacteriostatic: reversibly binds 30S subunit -> subunit distortion -> blocks bacterial translation -> stops proteins synthesis
• Spectrum: broad spectrum (GP and GN), good for atypicals
• SE: chelates Ca in teeth and bone (enamel dysplasia, decreased bone growth), GI discomfort, Candidiasis, allergy, N/V
• Elimination: faecal (used in renal impairment)
• CI: pregnancy, children <8yo
Would you use Amoxicillin to treat mycoplasma pneumonia?
- No, mycoplasma are small prokaryotes with NO cell wall -> do not gram stain and do not respond to most antibiotics (esp B lactams acting on cell wall)
- B-lactams include Penicillins, Cephalosporins, Carbapenems
Describe the treatment of atypical pneumonia?
Mild: - Amoxycillin (1g TDS PO x5-7days) - OR Doxycycline (100mg BD PO x5-7days) Moderate: - Benzylpenicillin (penicillin G) (1.2g IV QID) - AND Doxycylcine (100mg BD PO x7days) Severe: - Ceftriaxone (1g IV daily) - AND Azithromycin (500mg IV daily) - add Metronidazole (if considering aspiration anaerobes) - MSSA: Flucloxacillin - MRSA: Vancomycin - Influenza: Oseltamir
Describe the MA and SE of gentamycin?
Gentamycin- would cover atypicals BUT not 1st or 2nd line due to SE
o Class: aminoglycoside
o MA: bacteriocidal: irreversibly binds 30S subunit of bacterial ribosome -> inhibits formation of initiation complexes -> misreads mRNA -> interrupts protein synthesis
o Spectrum: mainly gram neg, synergistic effects w B-lactam abx, ineffective agains anaerobes (requires O2 for uptake)
o SE: nephrotoxicity, ototoxicity, neurotoxicity, neuromuscular problems (hypocalcaemia, hypomagnesaemia, hypokalaemia), elevated LFTs
o CI: pregnancy, lactation, renal impairment, sensorineural hearing problems, chronic liver disease
What causes abscess formation in pneumonia?
Abscess formation is a typical Staph aureus feature
3 enzymes:
1. Hyaluronidase: acts on hyaluronic acid (CT structural component) -> tissue breakdown -> pus collectino
2. Haemolysin: destroys RBCs
3. Coagulase: coagulates plasma -> limits bacteriocidal activity of blood
