Common Infections

CNS Infections

1) Meningitis:

  • When to do CT before LP? Focal neuro deficits, confusion, papilledema, seizures
  • What if CT is delaying LP? Start therapy
  • Most accurate Dx? Culture
  • MCC organism? pneumoniae, N. meningitides in adolescent
  • Most sensitive test? CSF protein (if neg -> meningitis ruled out)
  • Cell count
    • 1000s of neutrophils or positive gram stain -> bacterial -> ceftriaxone and vancomycin IV and steroids (lowers mortality)
    • 10-100s of lymphocyte, neg gram stain, neg culture -> cryptococcal, Lyme, rocky mountain spotted fever, TB, viral
  • Cryptococcal: in AIDs\low CD4 (<100) -> give amphotericin followed by life-long fluconazole, Dx: India ink or Ag, Ag change in response to therapy\not antibodies
  • Lyme: camping\hiking + target rash + 7th CN palsy + migratory arthritis -> give ceftriaxone
  • RMSF (rickettsia): camping\hiking+ rash moves in centrally\starts at wrists and ankles -> give doxycycline
  • TB: high protein CSF -> extend length of therapy + add steroids
  • In case of N. meningitides; close contacts exposure -> give Cipro or rifampin
  • Recurrent episodes of N. meningitides -> terminal complement deficiency
  • Elderly, leukemia, lymphoma, on steroids, HIV, alcoholic w\ bacterial meningitis -> add ampicillin (might have listeria)


2) Encephalitis:

  • Acute fever and confusion -> most likely due to HSV-1
  • Most accurate Dx: PCR (better than brain biopsy)
  • Rx: Acyclovir (Foscarnet if resistant herpes)


3) Abscess:

  • Fever and focal neurological deficit
  • CT: “ring” contrast enhancing lesion
  • If HIV -> treat for toxoplasmosis -> treat w\ Pyrimethamine + sulfadiazine -> repeat 10-14 days
    • if shrinks -> this is toxoplasmosis and complete therapy
    • if the lesion is the same -> biopsy (might be lymphoma)
  • If HIV negative -> go straight to biopsy


Head and Neck Infections

1) Otitis:

  • 40% Pneumococcus, 30% H. influenza, 20% M. catarrhalis
  • Most sensitive sign of otitis media: immobility of the tympanic membrane
  • If recurrent \ doesn’t respond to Rx -> do tympanocentesis for culture
  • Initial Rx: amoxicillin


2) Sinusitis:

  • Yellowish\greenish discharge, fever, headache, teeth pain, decreased transillumination
  • Most accurate Dx: culture of sinus aspirate\biopsy
  • Initial Rx: amoxicillin


3) Pharyngitis:

  • Sore throat, positive LN, exudate, no cough (lung), no hoarseness (laryngitis)
  • Best initial test -> rapid strep test
  • Most accurate Dx: culture = positive rapid strep test -> treat
  • A risk of GN and rheumatic fever
  • Rx: penicillin
  • If allergic to penicillin
    • Rash -> 1st gen cephalosporin
    • Anaphylaxis -> macrolides and clindamycin


GI Infections:

  • Bloody diarrhea: campylobacter, salmonella, shigella, E. coli, entaemba histolytica
  • MCC is campylobacter (associated w\ guillian-barre)
  • E coli and shigella -> HUS: hemolysis, high Cr, low plt (don’t give plt)
  • Shellfish and seafood -> vibrio
  • Dx: stool culture
  • Usually no Rx, you might give cipro
  • aureus + B. cerus -> vomiting
  • Giardiasis -> fresh water, campers\hikes, causes lacteal obstruction -> looks like fat malabsorption, Rx: metronidazole
  • Cryptospordiasis -> HIV (<200 CD4), on modified acid fast stain, Rx: raise CD4
  • C. difficile: Dx: toxin. Rx: metronidazole, if they get better and recurs -> retreat w\ metronidazole, if they didn’t get better -> treat w\ vancomycin


Urinary Tract Infections:

  • MCC is E. coli
  • Cystitis -> pyelonephritis -> abscess
  • Best initial test: U\A -> WBC is the most imp
  • Most accurate test: culture
  • Bacteria in urine is significant in pregnant ladies -> 1\3 will develop pyelonephritis
  • Rx:
    • Uncomplicated cystitis -> 3 days of TMP\SMX
    • Complicated cystitis (stones, strictures, obstruction, diabetics) -> 7 days of TMP\SMF
    • Preg or male -> 10-14 days of TMP\SMX (nitrofurantoin if preg)
  • Pyelonephritis -> ampicillin + gentamicin or Cipro or aztreonam
  • Most accurate test for abscess -> biopsy
  • Rx -> drain + antibiotics



Lyme’s Disease:

  • Rash, joint, neurological (MCC is bilateral 7th CN palsy), cardiac (MCC is AV block)
  • Lyme rash (target) = Lyme disease -> treat w\ amoxicillin or doxycycline
  • Other manifestations -> do serology first before treating
  • For joint and rash and 7th CN palsy -> oral amoxicillin or doxy
  • For neruo and cardiac -> IV ceftriaxone
  • If asx tick bite -> do nothing!


Sexual Transmitted Diseases:

1) Cystitis

Frequency urgency burning dysuria


2) Urethritis\cervitis:

Frequency urgency burning dysuria + discharge -> swab, culture and treat

Common infections 4

  • Rx: 1 gonorrhea drug + 1 chlamydia drug
  • If gonorrhea -> treat for chlamydia
  • If chlamydia -> don’t treat for gonorrhea


3) PID

Frequency, urgency, burning, dysuria + lower abdominal pain + cervical motion tenderness + high WBC -> same treatment

  • Best initial test? B-hCG (Exclude ectopic pregnancy)
  • Most accurate test? Laparoscope


4) Gonorrhea:

  • Asymptomatic in women, symptomatic in men (more complications w\ women)
  • Coinfection w\ chlamydia
  • Clinical features:
    • Men -> asymptomatic (10%: carriers), purulent urethral discharge, dysuria, erythema and edema of urethral meatus, freq of urination
    • Women -> asymptomatic (most), cervitis\urethritis: purulent discharge, dysuria, intermenstrual bleeding, dyspareunia
    • Disseminated gonococcal infection: fever, migratory polyarthritis, tenosynovitis, petechial skin rash, conjunctivitis, palatal hemorrhage
  • Dx: gram stain of discharge, culture,
  • Rx: Ceftriaxone (IM: 1 dose), if coexist w\ chlamydia: give its meds
  • Disseminated> hospitalize + ceftriaxone (IV or IM: 7 days)


5) Chlamydia:

  • MCC bacterial STD
  • Co infection w\ gonorrhea
  • Incubation period: 1-3 wks
  • Risk factor for cervical Ca
  • Clinical features:
    • Mostly asymptomatic (80% of women, 50% of men)
    • Women: purulent urethral discharge, intermenstrual or postcoital bleeding, dysuria
    • Men: dysuria, purulent urethral discharge, scrotal pain and swelling, fever
  • Dx: culture, enzyme immunoassay, PCR (not serology)
  • Rx: azithromycin (oral: 1 dose) or doxycycline (oral: 7 days)


6) Syphilis:

Painless ulcers (edges are raised) and painless hard nodes

  • Primary (genital chancre) -> do dark field; the most sensitive in primary
  • Secondary: (rash, mucus patches, alopecia, condylomata lata) -> do RPR\VDRL (100% sensitive in secondary)
  • Tertiary (neurological [dementia, personality, tabes dorsalis = post column degeneration], gummas formation, aortic aneurysm)
  • Rx:
    • For primary and secondary -> 1 IM shot of penicillin (doxycycline if allergic)
    • Tertiary -> IV penicillin (desensitize if allergic, neurosyphilis, or pregnant)

Common infections 5


7) Chancroid (H. ducreyi):

  • Painful genital ulcer, ragged borders, purulent base, unilateral soft tender inguinal LAP (buboes)
  • Rx: azithromycin (oral: 1 dose), ceftriaxone (IM: 1 dose)


8) Lymphogranuloma venereum (chlamydia):

  • Painless ulcer at inoculation site, painful nodes
  • Dx: serology
  • Rx: doxycycline (oral: 21 days)


9) Genital warts (HPV):

  • Anogenital warts (condylomata acuminata): cauliflower-like


10) Herpes simplex:

  • HSV-1: oropharynx lesions
    • Oral lesions: group of vesicles on patches of erythematous skin: Herpes labialis (cold sores) most common on lips (painful: heal in 2-6 wks)
    • Bell’s palsy
  • HSV-2: genital lesions:
    • Painful genital vesicles or pustules, tender inguinal LAP, vaginal\urethral discharge
  • Neonatal:
    • Congenital malformation, IUGR, chorioamnionitis, neonatal death
  • Dx: mainly clinical
    • Tznack smear (quickest): stain w\ Wright stain
    • Gold: culture
    • ELISA
  • Rx: for mucocutaneous ds: acyclovir for 7-10 days, foscarnet if resistant

Common Infections 6Common Infections 7Common Infections 8



  • Initial test to exclude osteomyelitis -> x-ray -> shows periosteal bone formation
    • If x-ray is negative -> get MRI (if you can’t do MRI -> do bone scan)
    • If x-ray is positive -> biopsy to determine abx (staph: oxcillin, MRSA: vancomysin or linezolid, gram neg bacilli (in diabetics): Cipro
  • How to follow treatment? ESR


Infective Endocarditis:

  • Fever + murmur
  • Janeway lesions: flat and painless
  • Osler’s nodes: raised and painful
  • Splinter hemorrhages
  • Roth spots in funduscope
  • MCC of death? Post infectious GN (antibodies clog up kidneys)
  • Best initial test? Blood culture
  • If negative -> if you have a risk, fever, embolic phenomenon, echo -> enough to dx
  • Empiric therapy? Vancomycin + gentamicin
  • If organism is S. bovis -> do endoscopy (bc associated w\ colon pathology)
  • Indication for surgery? Congestive failure, fungal, prosthetic, abscess, emboli
  • Prophylaxis? Significant cardiac defect (AS,MS,AR,MR,VSD) + bacteremia procedure (dental work w\blood, hemicolectomy, prostate biopsy, TURP)
  • For dental prophylaxis -> amoxicillin (clindamycin if allergic)
  • For GI procedure prophylaxis -> ampicillin (vancomycin if allergic)



  • CD4 < 200: PCP prophylaxis (TMP\SMX) if allergic -> dapsone (unless G6PD) or atovaquone
  • CD4 < 50: MAC prophylaxis (azithromycin)
  • Flu and pneumococcal vaccine for every HIV at any CD4
  • Antiretroviral S\E:
    • Anemia -> Zidovudine
    • Pancreatitis and peripheral neuropathy -> stavudine and didanosine
    • Kidney stone -> indinavir
    • Lomivudine has the least S\E, also effective against Hep B
    • Protease inhibitors -> hyper lipidemia and hyperglycemia
  • Regimens: 2 NRTI + either 1 PI or NNRTI
  • Efavirenz (NNRTI) is the only antiretroviral med contraindicated in pregnancy
  • When to start medication? CD4 <350 and high viral load
  • A pregnant woman with high CD4 (who doesn’t need meds for herself) -> give meds in the 2nd and 3rd trimester to prevent transmission -> and stop them after delivery
  • A pregnant woman with a viral load (> 1000) -> do C-section
  • Post exposure prophylaxis -> same regimen for 1 month
  • CMV in CD4 < 50 + blurring vision -> give ganciclovir (S\E: low WBC) or foscarnet (renal toxic)


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