General Infections




    Quick Reference Guide


    Staph + Strep

    1st line: Cephalexin 500mg PO qid x7d

    2nd line: cloxacillin 500mg PO q6h x10-14d

    or clindamycin 300mg PO q6-8h x10-14d, total <1.8 g/d

    In General:

    Cephalexin (Keflex) or Cefazolin (Ancef)

    -  Ciprofloxacin + clindamycin

    -  Amoxacillin + Clavulin (Big guns, if diabetes b/c atypicals, broad range)


    B-lactam Susceptible

    • S. pneumonia
    • H. influenza
    • Moraxella

    B-lactam non-susceptible

    • Atypicals (mycoplasma, legionella, chlamydia)

    -  New macrolide - If healthy, young, macrolide monotherapy (if low PORT)

    -  Azithromycin (atypicals) + ceftriaxone (S. pneumo + H. influ)

    -  Resp fluoroquinolone (moxiflox or Levoflox) broader range (if high PORT)


    E.coli (-)

    Staph Sapro (+)

    Klebsiella (-)

    Enterococcus (+)

    Proteus (-)

    Pseudomonas (-)

    -  TMP+TMZ  (25% E.coli resistance)

    -  Ciproflox (covers pseudomonas 25%res, maybe poor against enterococcus?)

    -  Nitrofurantoin (only cystitis, not pyelo, bad)

    For enterococcus

    -        Amoxacillin (covers enterococcus, maybe poor against pseudomonas?)

    -        Vanco, Ampicillin IV


    N. meningitimus

    Strep pneumo

    H. influ


    -  Pip-tazo (o.k CSF penetration, not great)

    -  Vancomycin (strep pneumo)+ ceftriaxone (all else)

    o   Add ampicillin for Listeria if elderly, alcohol, homeless)


    Bacteroides fragilis (anae)

    E.coli (aerobe)

    -  Metronidazole + ceftriaxone (or cipro)

    -  Single agent: pip-tazo, meropenem/ertapenem, moxifloxacin

    SSI prophylaxis


    -  Biliary tract: cefazolin

    -  Stomach/duodenum: cefazolin

    -  Small bowel: cefazolin

    -  Colin: cefazolin + metronidazole

    -  Appendectomy: cefazolin + metronidazole

    (Give 30min pre-op, give another dose if surg >4hrs)

    C.diff colitis

    Clostridium difficile

    -  Severe diarrhea, elevated WBC, 2nd to ABX administration

    -  Tx: oral flagyl or vancomycin

    Necrotizing fasciitis

    Type I: B-hemolytic Strep

    Type II: Polymicrobial

    -  Consider penicillin 4 million IU IV q4h

    -  Consider: clindamycin 900mg IV q6h  (GP, and anaerobes)

    Strep Pharyngitis Group A beta-hemolytic Strep


    PEN V 25-50 mg/kg/d PO div q6h x 10d

    amox/clav 45 mg/kg/d PO div. q12h x10d

    clarithromycin 15 mg/kg/d PO div. bid x10d

    azithromycin 12 mg/kg/d PO x5d


    pen V 500mg PO bid or 250mg qid x10d

    cefuroxime 250mg PO bid x4d

    clarithromycin 250mg PO bid x10d

    azithromycin 500mg PO once, then 250mg daily x4d

    If Penicillin allergy give erythromycin


    S. pneumoniae

    H. influenzae

    M. catarrhalis

    Group A Strep


    S. aureus

    1st line: amoxicillin 1g PO tid x10d

    (if penicillin allergey: TMP/SMX DS 1tab PO bid)

    2nd line: amox/clavulin 200/125mg PO bid x10d

    3rd line: clarithromycin XL 1000mg PO OD x10d

    Acute Otitis Media


    S. pneumoniae

    H. influenzae

    M. catarrhalis


    1st line: amoxicillin 75-90 mg/kg/d PO tid x5d

    2nd line: amoxicillin/clavulin

    3rd line: macrolides


    amoxicillin 500mg PO tid x7-10d

    Penicillin allergy: cefuroxime, azithromycin, clarithromycin

    Spinal Infection

    epidural abscess etc..

      3rd gen cephalosporin +/- ampicillin +/- vancomycin
    • First line: ceftriaxone 250mg IM + azithromycin 1g PO (for chlamydia, which is often concurrent)
    • Second line: cefixime 400mg PO + azithro 1g PO
      • OR spectinomycin 2g IM +azithro 1g PO
      • OR azithromycin 2g PO



    Bacteria` Mgmt
    MRSA Cloxacillin + TMX



    • Viral Causes
      • Parainfluenza
      • Adenovirus
      • RSV
      • Rhinovirus
      • Enterovirus
    • Bacterial causes:
      • Strep pyogenes (Group A strep)

    Pulmonary Infections

    • Common organisms:
      • PnCAPcauses.pngStreptococcus pneumoniae
      • Haemophilus influenzae
      • Mycoplasma
      • Chlamydia pneumoniae
    • Other pathogens:
      • Staph aureus
        • often ventilator associated pn.
      • Gram negatives
        • uncommon, unless lung disease or alcoholism. (reduced gag reflex). Usually hospitals and nursing homes.
      • Legionella
        • vary with seasons and geography.
      • Anaerobes
        • often aspiration pneumonias.
      • Viral
        • influenza, parainfluenza, respiratory syncitial virus (RSV).
    • Risk Factors:
      • Viral infections  (damage cilia)
      • Smoking (damange bronchial cells)
      • Alcohol (depresses coughing and epiglottis)
      • Elderly (decrease dhumoral and cell mediated immunity)
      • Immunosuppressed
      • Chronic diseases
      • Cold weather (dries up mucous)
    • Classified as:
      • Typical Pneumonia
        • Rapid onset, severe symptoms, productive cough, dense CXR consolidation.
      • Atypical Pneumonia
        • Slower onset, less severe symptoms, less severe cough, minimal sputum, CXR (patchy/interstitial pattern)
      • Community Acquired (<14d in hospital)
      • Hospital Acquired (>14d)
    • Can sometimes narrow down to organism by symptoms and radiologic findings.
    • PnByOrganism.png
    • On history/exam, inquire about:
      • Cough - type of sputum (S. pneumon is rusty colored, red current jelly color is Klebsiella etc..)
      • Chest discomfort
      • Rigor - classically one teeth-chattering chill is Strep. pneumo.
      • Shortness of breath
      • Neck stiffness - r/o meningitis
    • Chest Xray findings:
      • Lobar Pneumonia
        • Distinct anatomic segment of the lung.  Respects anatomic boundaries (no proteases/hyaloronidases to break down tissue).
        • S. pneumoniae, H. influenzae, Legionella
      • Bronchopneumonia
        • Originates in small ariways and spreads to adjacent ones.  "Patchy infiltrates" that involve multiple areas of the lung and extend down bronchi. 
        • S.aureus, Gram negatives, Mycoplasma, Chlamydia, viruses
      • Intersitial pneumonia
        • Lung interstitium inflamed: fine diffuse grandular infiltrate.
        • Influenza, CMV, Pneumocystis jirovecii, Miliary TB (micronodular infiltrates).
      • Lung abscess
        • Tissue necrosis, cavities with inflammatory fluid
        • Anaerobics and S.aureus.
      • Nodular Lesions
        • Yeasts: (cryptococcus) Moulds (Histoplasmosis, coccidiomycosis) - nodular
        • "Cannonball lesions" from hematogenous spread of endocarditis.


    • Virulence Factors: Enterotoxin, cytotoxin.
    • Types:
      • Watery Diarrhea (ETEC)
        • Enterotoxigenic E.coli.
      • Bloody Diarrhea (others)
        • EHEC - Enterohemorrhagic E.coli (O157:H7) --> HUS.
        • Salmonella
        • Shingella
        • Campylobacter
        • Yersinia
    • Hemolytic Uremic Syndrome (HUS) --> E. coli O157:H7
    • Fecal-Oral spread (contact)


    Necrotizing Fasciitis

    • Rapidly spreading, painful, infection of deep fascia + necrosis
    • Pain out of proportion, beyond erythema, late findings (skin blue/black, bullae, gangrene, subq emphysema)
    • Etiology:
      • Type I : B-Hemolytic Strep (GAS?)
      • Type II: Polymicrobial (less aggressive)
    • Clinical diagnosis (can do hemostat)
    • Tx:
      • Resuscitation
      • Surgical debridement, copius irrigation
      • IV abx: penicillin 4million IU IV q4h or clindamycin 900 mg IV q6h
      • Consult ID


    Approach to Cellulitis

    • Typically caused by S. aureus or GAS.  Unless if Diabetes, can also be caused by anerobics.
    • R/O MRSA, risk factors:
      • Hospital Acquired MRSA (ICU or hospital stay)
      • Community Acquired MRSA
        • Community prevalence: i.e. Arizona (Most cellulitis is MRSA from abx overuse)
        • Prison stay, or contact w prison stays
        • Homeless
        • Contact sports (Wrestling, Football)
    • If suspicious for MRSA add Septra or Vancomycin.  Can also use clindamycin, but ~10-20% MRSA resistance to clinda.  Usually use clindamycin if toxic shock (stop protein synthesis to stop toxin production).
    • If no improvement with 48h of ancef/keflex
      • Abscess/Collection?  - drain
      • Free air?  anaerobics gas prodcucing- do Xray to see pockets of air.   Then cover for anaerobics.
      • Foreign body - Xray
      • Resistance (MRSA - check risk factors)
      • Diabetes? - vascular insufficiency.
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