Infectious Disease Flashcards
Osteomyelitis gen info
Bone infection –> inflammatory destruction of bone
Two categories:
- hematogenous, secondary to sepsis
- direct spread of bacteria
> adjacent infection (infected diabetic foot ulcer, decubitus ulcer)
> trauma (open fx)
> vascular insufficiency (PVD)
MC microorganisms: s. aureus, coagulase-neg staphylococci
Can involve any bone, commonly; long bones, foot/ankle, vertebral bodies
OM of vertebral body d/t TB –> pott disease
chronic OM –> bone necrosis + soft tissues compromise or relapse of previous OM, vey challenging to tx, almost impossible to completely eradicate
Osteomyelitis risk factors (complications or chronic)
open fx
DM
IVDU
sepsis
Osteomyelitis clinical features
pain over involved area of bone mc
localized erythema, warmth, swelling
systemic sxs; fever, headache, fatigue
draining sinus tract thru skin in chronic disease
Osteomyelitis diagnosis
WBC count
ESR, CRP (monitoring response to therapy)
Needle aspiration or bone biopsy (OR) - most direct/accurate diagnostics (+culture)
plain radiograph - early changes like periosteal thickening or elevation show up after 10 days, lytic lesions = advanced dz
MRI - most effective + assess extent of disease
Osteomyelitis treatment
IV abx 4-6 weeks
- start only after microbial etiology is narrowed based on cultures or if HDU
- empiric therapy; abx w high bone penetration like cephalosporins (cefazolin, ceftriaxone, cefuroxime), FQs (levofloxacin, ciprofloxacin, moxifloxacin), vancomycin, linezolid, daptomycin, clindamycin (+- rifampin adjunct for biofilm penetration)
- add aminoglycoside +- beta lactam if possibility of gram neg infection
- surgical debridement of infected necrotic bone
Septic Arthritis gen info
microorganisms (usu bacteria) invade joint space (not bone itself) & release endotoxins–> trigger cytokine release and neutrophil infiltration –> inflamm response leads to erosion + destruction of joint
Pathogenesis: microorganisms penetrate joint space by;
- hematogenous spread mc
- contiguous spread from another locus of infxn (OM, abscess, cellulitis)
- traumatic injury to joint
- iatrogenic (arthrocentesis, arthroscopy)
Microbio
- bacteria mc; s. aureus mc, strep, n. gonorrhoeae, consider gram neg like pseudomonas, salmonella if hx of sickle cell disease, immunodeficiency, or IVDU
Risk factors
- prior joint damage (RA)
- joint prothesis
- DM
Septic Arthritis clinical features
Swollen, warm, PAINFUL joint (painless rom of involved joint –> septic arthritis very unlikely even w erythema. Any micromotion causes severe pain usu)
- ROM active/passive very limited
+- effusion
fever, chills, malaise
MC joint = knee
immunosuppression or connective tissue dz +- polyarticular arthritis
gonococcal arthritis
acute mono or oligoarthritis progressing within days in a migratory or additive pattern; knees, wrists, hands, ankles mc
tenosynovitis in hands/feet
fever, chills, rash (macules, papules, +- pustules) = disseminated gonococcal infection - admit
Aspirate joint, abx + doxy (chlamydia)
consider HIV, syphilis testing
Septic Arthritis diagnosis
joint aspiration + analysis of synovial fluid in everyone suss of septic joint:
- wbc with diff; >50,000 wbcs >80% PMNs
- gram stain
- culture aerobic + anaerobic
- crystal analysis; acute gout is mimicker
- PCR synovial fluid; if high suss but above neg
blood cultures
elevated ESR/CRP, leukocytosis
xrays - not very useful unless severe
CT/MRI if sacroiliac or facet joints involved
appropriate mucosal surface cultures (GU)
Septic Arthritis treatment
prompt abx tx
- don’t delay in starting if suss
- treat empirically until culture results come back
healthy w s.aureus –> parenteral oxacillin or first gen ceph x 4 wks
- treat w vanc if mrsa suss
Immunocomp –> parenteral, broad-spectrum w gram neg coverage; third gen ceph, aminoglycoside 3-4 wks
drainage
- daily aspiration as long as effusion persists
- vs surgical drainage recommended
HIV related illnesses
Opportunistic infections: Pneumocystis pneumonia Tuberculosis Toxoplasmosis Disseminated MAC Bartonella spp, Candida spp, Coccidioides spp (coccidioidomycosis) Cryptococcus spp, Cystosporidium, cytomegalovirus, varicella-zoster virus, and Histoplasma capsulatum.
Lyme Disease general info
3 major endemic areas in US:
NE seaboard (maine to MD)
Midwest (north central states like Minnesota, Wisconsin)
West Coast (northern California)
incubation period = 3-32 days
Transmission cycle:
Arthropod-borne disease d/t borrelia burgdorferi (gram negative spirochete) spread by deer tick mc in spring/summer. Transmission more likely if tick engorged or attached >72 hrs.
Lyme Disease sxs
Stage 1: early, localized infection
- erythema migrans with central clearing (bull’s eye target) around bite within a month of bite +- viral-like syndrome.
- large, painless, well-demarcated commonly on thigh, groin, or axilla
- multiple lesions = hematogenous spread (below)
Stage 2: early, disseminated 1-12 wks
Infection spreads via lymphatics/bloodstream within days to weeks after erythema migrans
sxs: intermittent flu-like sx; headaches, neck stiffness, fever/chills, fatigue, malaise, msk pain
After several weeks, 15% develop at least one of:
meningitis (PE signs negative)
encephalitis
cranial neuritis (often bilateral facial nerve palsy)
peripheral radiculoneuropathy (motor or sensory)
After weeks - months of onset, 8% will have cardiac manifestations (AV block mc, pericarditis, arrhythmias)
Stage 3: late, persistent infection (months to years after initial infection)
- arthritis mc, esp large joints (knee)
- chronic CNS disease; subacute, mild encephalitis, transverse myelitis, axonal polyneuropathy
- acrodermatitis chronica atrophicans (a rare skin lesion); reddish purple plaques and nodules on extensor surfaces of legs
Lyme disease diagnosis
clinical diagnosis: erythema migrans + tick exposure > lab confirmation + treat empirically
serologic studies: ELISA to detect serum IgM and IgG antibodies during the first month. Western blot to confirm positive or equivocal results
Lyme disease treatment
Early localized disease:
confined to the skin - abx for 10 days
evidence of spread beyond the skin - extend to 20-30 days
Early lyme disease:
oral doxy x 21 days
amoxicillin and cefuroxime are alternative
erythromycin for preggos with penicillin allergies
Tx of complications (facial nerve palsy, arthritis, cardiac disease): prolonged abx x 30-60 days
Meningitis or other CNS complications: IV antibiotics x 4 weeks.
Rocky mountain spotted fever general info
Intracellular bacteria: Rickettsia Rickettsii
Ticks feeding on various mammals are vectors for transmission of disease
Major endemic areas: SE, midwestern, western US
Peak incidence: spring/summer months
patho: organism enters host cells via tick bite > multiply in vascular endothelium + spread to different layers of vasculature > damage to vascular endothelium > increased vascular permeability > activation of complement, microhemorrhages, microinfarcts
Rocky mountain spotted fever sxs
Sxs start 1 week after tick bite
Sudden onset of fevers, chills, malaise, myalgias, photophobia, headache, n/v
4-5 days of fever > papular rash starting peripherally (wrists, forearms, palms, ankles, soles) then spreads centrally (limbs, trunk, face) > becomes maculopapular then petechial
May lead to interstitial pneumonitis
Rocky mountain spotted fever dx
primarily clinical
+- elevated LFTs, thrombocytopenia
Acute and convalescent serology and immunofluorescent staining of skin biopsy are confirmatory
Rocky mountain spotted fever tx
doxycycline ~7 days
IV if patient vomiting
chloramphenicol for CNS manifestations or pregnant patients
Epidural Abscess gen info
Contained purulent infection of the CNS.
Epidural abscesses may be either spinal or intracranial.
Bug: s aureus mc, strep, gram neg bacilli (e coli)
Both rare however incidence of spinal epidural abscess rising d/t spinal surgeries/interventions, indwelling IV catheters + assoc bloodstream infections, IVDU, immune system suppression.
Prompt diagnosis/management critical as delay in therapy may lead to permanent neuro damage.
Rfx: spinal procedures, IVDU, tattoos, sinus infection, URI, OM
Epidural Abscess SXS
Spinal epidural classically: fever, back pain, progressive focal neurologic compromise (parasthesias, radicular pain, sensory/motor deficits, meningismus, loss of bladder/bowel function
Intracranial epidural abscess: fever, global or focal CNS dysfunction. +- neck pain, URI sxs
Red flags: cauda equina syndrome
Epidural Abscess DX
classic presentations are rare, need a high index of suspicion and knowledge of risk factors
suspect SEA in patients with fever + back pain
suspect ICEA in patients with fever, AMS wwo focal neuro deficits
MRI preferred to localize + see extent, baseline labs, ESR/CRP, blood cultures before tx
Epidural Abscess TX
Combined surgical and medical therapy needed for almost all cases
SEA: emergent surgical decompression if with neuro compromise (early decompression improves outcomes). Start abx before surgery > covering both MRSA and gram-negative bacilli (ceftazidime or cefepime)
culture results determine definitive abx tx > 6-8 weeks
Cellulitis gen info
Inflammatory condition of skin and subQ tissue
Caused by a wide variety of bacteria, mc group A strep or S. aureus > often bug based on history
Bacteria gain entry thru breaks in skin: IVs, incisions, immersion in water, bites, wounds
chronic conditions: venous stasis diseases, lymphedema, diabetic ulcers
if untreated can lead to bacteremia
first determine purulent vs nonpurulent > severity of cellulitis based on presentation
Cellulitis sxs and dx
inflammation: erythema, warmth, swelling, pain +- fever
clinical dx
blood cultures if w fever
tissue cx if w wound, ulcer, or site of infection
imaging (plain film, MRI) if suspicion of deeper infection
Cellulitis tx
base treatment on suspected pathogen from hx
most require parenteral abx
should cover group A strep and MSSA (oxacillin, cefazolin)
MRSA only if suspected (vanc)
Continue IV abx until signs of infection improve then oral abx for 2 weeks
Necrotizing fasciitis
Life-threatening infection of deep soft tissues that rapidly tracks along fascial planes.
extension of infection > thrombosis of microcirculation > tissue necrosis, discoloration, crepitus, and cutaneous anesthesia.
erythema & extreme pain out of proportion to PE → blue hemorrhagic bullae (blisters at site) → gangrene → septic shock +- crepitus. (Fournier gangrene - in the perineum +- scrotal involvement esp w impaired immunity (DM) after trauma to area.) lrinec score
May rapidly progress to sepsis, toxic shock syndrome (TSS), multi-organ failure.
Bug: s pyogenes, clostridium perfringens
Rfx: recent surgery, diabetes, trauma, IVDU
SXS: fever, pain out of proportion to appearance of skin in early stages > high index of suspicion
TX: abx alone not sufficient, NEED RAPID SURGICAL EXPLORATION AND DEBRIDEMENT
Broad spectrum parenteral abx tx
(carbapenem or pip tazo + MRSA coverage eg vancomycin or daptomycin + clinda)
GNR Bacteremia gen info
Common sources: UTIs, intra-abdominal infections like colitis or cholangitis, pneumonia, central venous catheters
Bugs: E.coli, klebsiella pneumoniae, enterobacter spp, pseudomonas aeruginosa
Rfx: immune compromise, presence of indwelling catheter, recent abx use, housing in long term care facility, healthcare contact
Gram-negative pathogens a/w rapid systemic response due to endotoxin production
endotoxin (lipopolysaccharide) comprises about 75% of the outer membrane of GNRs > potent inducer of host defense cells, leading to
systemic inflammation: activation of proinflammatory mediators, hypotension, tissue damage, organ dysfunction, activation of coagulation cascade.
High levels of proinflammatory cytokines, tumor necrosis factor, and vasodilators lead to
apoptosis of endothelium cells in multiple organs,
increased vascular permeability and hypotension
hypoperfusion, manifesting as lactic acidosis, oliguria, and/or altered mental status
alterations in temperature
leukocytosis
tachycardia
tachypnea
depressed ventricular ejection fraction
GNRs
Klebsiella species Escherichia coli Enterobacter species Pseudomonas aeruginosa Haemophilus influenzae Acinetobacter species Neisseria meningitidis Proteus species Salmonella species Serratia species Brucella species Campylobacter species
GNR Bacteremia SXS
SIRS; fever, rigors, sweats, tachycardia, tachypnea, hypotension, AMS
Onset and shock may be rapid
GNR Bacteremia DX
Blood cultures
Evaluation should include careful search for source of infection
Obtain follow-up cultures at 48-96 hours to document response to treatment
Most pathogens yield cx results within 48 hrs
GNR Bacteremia TX
empiric abx asap
combination therapy when Pseudomonas or multi-drug resistant organism suspected
remove, drain, or debride any potential sources of infection like vascular or urinary catheters, intra-abdominal abscesses, obstructive cholangitis
duration of therapy varies with pathogen, adequacy of source control, and patient characteristics
GNR or pseudomonas abx coverage
pip-tazo cefepime, ceftazidime imipenem, meropenem aztreonam cipro, levofloxacin gentamicin, tobramycin, amikacin polymyxins
S. Aureus bacteremia gen info
MC of bacteremia
Result from breaches in skin; indwelling catheters, post surgery, local infection like pna or cellulitis
Common complications > metastatic infections like endocarditis, embolization to CNS or other visceral organs, vertebral osteomyelitis, other bone/joint infections
S. Aureus bacteremia SXS
Vary from asx to fever alone to sepsis
S. Aureus bacteremia DX
2 sets of blood cx collected before abx
Evaluation should include a careful assessment for the source of infection, any potential removable foci of infection, such as an indwelling line, or metastatic sites of infection.
Echo if suss for IE
S. Aureus bacteremia TX
Prompt source control and abx
Removal and/or debridement of any source or metastatic focus of infection, such as drainable abscesses and indwelling foreign bodies
MSSA: oxacillin, nafcillin, or cefazolin (if normal renal fxn)
MRSA: vancomycin, daptomycin
Minimum 14-day course can be considered in patients who defervesce and clear bacteremia within 72 hours, have no evidence of complications, and do not have indwelling catheters or prosthetic material, underlying malignancy, or immunocompromise.
All others should be treated with 4-6 weeks of antibiotics.
Syphilis
path: t. pallidum
1: singular ulcer
painless
+LN non-tender
2: fever + rash
targetoid
palms/soles
3: neurosyphilis
tabes dorsalis
argyll robertson
DX
1: darkfield microscopy
2: RPR > FTA-ABS
3: LP > CSF RPR > CSF FTA-ABS
TX
1: PCN x 1 IM
2: PCN x 1 IM
EL: PCN x 1 IM
LL: PCN IM qwk x 3 wks
3: PCN IV q4h x 10-14 days
LGV
Lymphogranuloma venereum (LGV) is a sexually transmitted infection caused by a particular strain of chlamydia bacteria
path: c trachomatis
singular
painless
+LN tender
suppurative, drainage
DX: NAAT
TX: doxy
Chancroid
path: h. ducreyi
singular
painful
+LN tender
dx: gram stain + cx
tx: azithro or cipro
Herpes
path: hsv1, hsv2, DRG
painful burning prodrome
painful vesicles on erythematous base
coalesce = ulcer
dx: pcr
tx: acyclovir or valacyclovir
