Infectious Diseases – ED

Infectious Diseases

1. Given a patient with a suspected severe infection, use empiric antibiotics early, before completing investigations.

2. In a patient with serious systemic infection, look for and recognize septic shock and treat septic shock aggressively when found, using a structured approach (i.e., goal-directed therapy in addition to antibiotics).

3. Given a patient who presents with signs and symptoms of infection, look for and identify risk factors for more serious or more complicated infections (e.g., immunocompromised, age, comorbidity, travel, alcohol and substance use).

4. In a patient with an apparent minor infection, look for and identify complications or more serious but less overt diagnoses (e.g., pharyngitis versus peritonsillar abscess, cellulitis versus necrotizing fasciitis, vaginitis versus STI or PID).

5. In a patient with non-specific presentations such as altered mental status, fatigue, or weight loss, include infection in the initial differential diagnosis and consider some less common etiologies (e.g., malaria, tuberculosis, endocarditis, Lyme disease).


  • Borrelia burgdorferi (ixodes deer tick)
  • risk of infection if attach >72hr
  • Stage 1 (early)
    • erythema migrans (annular, expanding, with central clearing) – 60-80% cases 2-20 days after bites
    • Malaise, headache, fever, arthralgias, resolves in a month
  • Stage 2 (early disseminated)
    • dissemination days to 6mo, secondary annular lesion (50%)
    • Fever, adenopathy
    • Neuro:
      • Cranial neuritis – uni/bilateral CN 7 palsy – can also occur w/ initial EM
      • Neuroborreliosis: H/A, neck stiff, AMS, ataxis, myelitis, encephalitis, radiculoneuritis, mononeuritis multiplex
    • Arthritis – oligo, asymmetric, large joints – knee
    • CV – AV block, myopericarditis
  • Stage 3 (late disseminated)
    • years post exposure
    • chronic migratory arthritis, chronic CNS dz, chronic dermatitis
  • Tx – doxycycline 100 bid for 14-21 d (amoxicillin <8yo, pregnant)
    • doxycycline 1st line for peds in RMSF
  • Prophylaxis with tick bite in endemic area and tick feeding >72hr / partially engorged tick – doxycycline 200mg x 1 dose (ok for peds too)


  • protozoal – plasmodium; anopheles mosquito
    • plasmodium falciparum: RBC of all ages, high chloroquine resistance, highest mortality
    • plasmodium vivax – young RBC & reticulocytes; dormant exoerythrocytic stage in liver
    • plasmodium malariae / ovale
  • incubation 8-30d, malaise, fever, headache –> severe F/C/N/Weak (10-40% afebrile at presentation)
    • repetitive 48-72hr cycles of fever – pathognomonic for P. vivax/ovale/malariae
    • GI – mod splenomegaly (prone to rupture at late stages), tender hepatomegaly
    • CNS – cerebral malaria: coma, Sz, AMS, 20% mortality
  • Dx: thick (sensitive) and thin blood smears
    • normocytic anemia w/ hemolysis; thrombocytopenia w/o leukocytosis
    • Giemsa stain – parasites / crescent-shaped gametocytes
    • smear repeat in 12-24hr if initial smear negative & index of suspiciion
    • elevated ESR, false positive VDRL, HypoNa, hypoglycemia
  • Tx: ABC
    • admit known or suspected P. falciparum
    • IV quinine gluconate + doxycycline
      • AMS, Renal failure, Resp distress, Sz, shock, severe anaemia
      • P. falciparum >4% of visible RBC
    • P. vivax, ovale, malariae – chloroquine + primaquine po x 14 d; hydroxychloroquine, quinine + doxycycline, malarone (atovaquone-proquanil)
  • Prophylaxis – chloroquine 500mg weekly
    • Malarone if areas with chloroquine resistance

Tuberculosis (TB) – mycobacterium tuberculosis – acid-fast aerobic rods; airborne droplet

  • predisposing factors:
    • urban dwellers, homeless, nursing home, prisoners
    • alcoholics, HIV, elderly, drug users
  • Primary tuberculosis
    • airborne infection, middle/lower lung, often asymptomatic
  • post-primary (reactivation) tuberculosis
    • invovles apical/posterior segments of upper lobe (inc O2)
  • Extrapulmonary tuberculosis (15% worldwide)
  • Latent infection
    • extrapulmonary spread w/ positive skin test and no clinical dz
    • reactive when host immune unable to contain organism
    • at risk for progession – elderly, HIV, leukemia, solid organ carcinoma, transplants, DM, ESRD, silicosis
  • TB is an AIDS-defining illness in HIV pt
    • may be initial clinical manifestation of HIV
    • high rate of false negative skin test
  • MDR-TB
    • highest incidence in immigrants
    • resistance to INH and rifampin
    • high cure rate with early dx and 4-6drug therapy for 18-24mo
  • XDR-TB
    • resistant to INH, rifampin, second line drugs
    • highly associated w/ HIV
    • TDR-TB reported in India
  • Presentation
    • low-grade fever, night sweats, fatigue, anorexia, wt loss
    • Resp: cough, productive of mucouid, hemoptysis, pleuritic chest pain
    • extra-pulm: adrenals, bones, joints, GIGU, LN, meninges, pericardium, peritoneum, pleura
  • Dx
    • Mantoux PPD skin test: 0.1ml PPD sc and read 48-72hr post – requires immunocompetent patient
    • CXR: primary (unilateral hilar), reactivation (apical/upper lobes), miliary (1-3mm nodules + effusion)
    • Cultures – gold standards, 1-6wk
      • sputum, gastric lavage, tissue sample, body fluids
    • Acid-fast stain of sputum – rapid and positive in 50-80% TB
    • Quantiferon gold TB test – results in 24hr – 95% senstiive/specefic
  • Tx –  respiratory isolation (negative pressure, mask on pt, N95)
    • HCW-supervised 4 drugs regimen x 2mo until susceptibility test available: RIPE (Rifampin, INH, Pyrazinamide, Ethambutol/streptomycin)
    • direct observe therapy to ensure compliance
  • Admission – resp compromise, MDS-TB, social circumstance

6. In a patient who presents with signs and symptoms of infection of an unknown focus, include in the physical examination the appropriate specific assessment of commonly neglected areas (e.g., neck stiffness, skin signs in the elderly, vaginal and pelvic examination, foreign bodies in orifices or wounds).

7. Given a patient with a fever of unknown cause, adapt the investigation to the age and the clinical context and do not either over- or under-investigate.

8. Given a patient with a clinically identified bacterial infection, prescribe appropriate antibiotics based on clinical information (e.g., probable pathogens for age and clinical context, resistance patterns) before culture results.

9. Do not use antibiotics for a clinical presentation of infection that is most likely non-bacterial, such as a viral upper respiratory infection.

Pharyngitis – The modified (age) Centor criteria

  • Fever
  • Sore throat with no cough
  • Anterior cervical LN
  • Tonsillar exudate
  • Age: 3-14 +1, 15-44 = 0, >44 = -1

10. In a patient with a diagnosed infection or exposure, assess the need for and arrange post-exposure prophylaxis for the patient and others, when appropriate (e.g., post-needle sticks, communicable diseases, rabies, tetanus).

Post-needle sticks

  1. HCV – no prophylaxis recommended – Ig not beneficial
  2. HBV – HBsAg / HBeAg source higher risk
  3. HIV – considered in all occupational and non-occupational exposures
    1. rapid HIV to determine source status
    2. If rapid HIV test n/a, PEP ASAP & 72hr f/u if source HIV negative
    3. PEP – Raltegravir, Truvada

Meningococcemia – Neisseria Meningitidis / droplets

  • F/C/Malaise/myalgia/weak/N/V/URI/HoTN/Shock
  • Petechiae (DIC), urticaria, hemorrhagic vesicles, macules/papules:  extremities/trunk +/- palms/soles/head/mucous membrane
  • Severe H/A, stiff neck, AMS
  • DDX: RMSF, TSS, Endocarditis, TTP, HSP, DIC, disseminated gonococcemia
  • Dx: Blood cultures, skin cultures, CBC, Coag, Gran stain, serology, LP
  • Tx: airway, IVF, IV steroids, ceftriaxone 2g IV
  • prophylaxis for close contacts (4hr) – Ciprofloxacin, ceftriaxone, rifampin

Pertussis – bordetella pertussis – toxin-mediated / aerosolized droplets

  • catarrhal stage: URI, min F
  • Paroxysmal stage (1-6wk): paroxysmal staccato cough worse at night, whoop (inspiratory stridor at end of cough), Cyanosis, post-tussive emesis
  • Convalescent stage (wk-mo): gradual resolution
  • Dx: cough >2wk, whoop, paroxysms, post-tussive emesis
    • NPS, ALC>20,000
  • Tx: supportive, azithromycin
  • Immunization DtAP, Tdap
  • Tx close contacts

Tetanus – clostridium tetani

  • inhibits GABA / glycine release – generalized muscle rigidity / contractions
  • toxin – hematogenous to peripheral nerve, then retrograde to CNS
  • Local tetanus: muscle rigidity, resolves wks-mos
  • Generalized tetanus – pain, stiff / rigid jaw / facial muscle, progress down
    • Trismus, dysphagia, opisthotonos, fist clenching
    • Normal sensorium (altered in rabies)
    • Autonomic -hypersympathetic: tachycardia, HTN, diaphoresis
  • DDx: strychnine, dystonic reaction, hypoCa, Meningeal irritation, rabies
  • Tx: ventilator / muscle relaxation
    • Wound debridement after TIG (inject around wound)
    • Tetanus IG infiltrate wound
    • Autonomic dysfunction – labetalol, Mg, Clonidine, morphine

Rabies – rhabdovirus

  • inoculation w/ saliva from infected animal; bites proximity to CNS a factor (retrograde through peripheral nerve)
  • Bats, raccoons, skunks, foxes, cats, cattle, dogs
  • Clinical course
    • Prodrome (F/malaise/H/A), pain & paresthesia at bit site
    • Excitation phase: inc motor activity, excitation, agitation, hypersensitivity, fever, paralysis
    • Brainstem dysfunction: dysphagia, hydrophobia, paralysis
    • Classic (furious) form: agitation, AMS, muscle spasm, opisthotonos
    • Paralytic rabies: ascending, symmetric flaccid paralysis
    • Mortality: pituitary dysfunction, Sz, Resp failure, cardiac dysfunction, renal failure, bacterial superinfection, autonomic dysfunction
  • DDX: tetanus, polio, GBS, transverse myelitis, CVA, anticholinergic, encephalitis
  • Tx: supportive – airway
  • Postexposure prophylaxis
    • offered in rabies-prone exposures unless animal can be observed for 10 days or sacrificed and tested
    • Depends on location, animal, animal Imm, exposure circumstances
    • Recommended for any potential bat exposure
    • Regimen: Human diploid cell vaccine day 0,3,7,14 + HRIG 20IU/kg around wound and IM
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CCFP ExamApril 30, 2015
The big day is here.
September 2020
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