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Infectious Disease

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What is the difference between cellulitis and erysipelas?

  • Erysipelas usually on face with very distinct borders

  • Cellulitis involves deeper dermis and sub-q fat, borders less distinct

 

What underlying conditions should be treated to prevent recurrent cellulitis?

  • Tinea pedis, lymphedema, chronic venous insufficiency

 

What are some antibiotic options for nonpurulent cellulitis without and with systemic infection?

  • Without: oral PCN, amoxicillin, cephalexin, clindamycin

  • With: IV PCN, CTX, cefazolin, clindamycin

 

What are antibiotics options for purulent cellulitis that is mild/moderate vs severe?

  • Mild/moderate: Bactrim, doxycycline

  • Severe: IV Vanc, Linezolid, daptomycin, ceftaroline

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Hematogenous-spread osteomyelitis typically affects what structure?

  • Vertebral bodies

 

When should underlying chronic osteomyelitis be considered?

  • When chronic wounds do not heal/respond to appropriate therapy 

 

What lab markers can help with diagnosis and be used to track response to treatment?

 

What should be the initial imaging?

  • X-ray but if negative does not rule it out if high suspicion

  • MRI preferred if x-ray nondiagnostic

 

Management?

  • If patient stable obtain bone biopsy prior to starting antibiotics

  • Surgical debridement if extensive

  • 4-6 weeks of antibiotics for acute infections, may require longer course if chronic

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Most common culture results from diabetic foot infections?

  • Polymicrobial 

 

Management of diabetic foot infections?

  • Imaging for any new infections, culture from deep probing or biopsy, assess for arterial insufficiency, surgical consultation

  • Mild/nonpurulent: oral cephalexin, augmentin, clindamycin

  • Mild but purulent or risk for MRSA: oral doxy, or bactrim plus beta lactam

  • Moderate or severe: IV b-lactam/b-lactamase inhibitor combos, carbapenems, or flagyl plus a fluoroquinolone, or third generation cephalosporin with Vanc/dapto/linezolid

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What qualifies a patient as having severe C. Diff? 

  • WBC > 15 and/or Cr > 1.5

 

What is first-line treatment for an initial episode of C. Diff?

  • For non-severe C. Diff, first-line treatment is with either Fidaxomicin or PO Vancomycin, with a preference towards Fidaxomicin if possible per 2021 IDSA Guidelines

  • For severe C. diff, first-line treatment should be Fidaxomicin over PO Vancomycin if possible

  • 2021 IDSA Guidelines suggest Fidaxomicin over Vancomycin based on evidence suggesting reduced recurrence rates, but no difference in initial cure or mortality (https://www.idsociety.org/globalassets/idsa/practice-guidelines/cdi-2021-focused-update.pdf)

  • However, cost is a very important practical consideration that may limit ability to used fidaxomicin

 

What qualifies as fulminant C. Diff? 

  • Shock, toxic megacolon, ileus

 

How do you treat fulminant C. Diff?

  • Without ileus, treatment is with PO Vancomycin (500 mg QID) plus IV Metronidazole (500 mg q8)

  • One retrospective study found addition of IV Metronidazole in critically ill C. Diff patients was associated with reduced mortality (https://pubmed.ncbi.nlm.nih.gov/26024909/)

  • With ileus, treatment is also with PO Vancomycin plus IV Metronidazole BUT with the addition of fecal transplant if available OR rectal Vancomycin

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What are the indications for antibiotic ppx?

  • Tick attached >36 hours

  • Presenting within 72 hours of tick removal 

  • Tick is black-legged deer tick

 

What is the treatment according to stages?

  • Early localized: doxycycline for 10-21 days, amoxicillin or cefuroxime for 14-21 days

  • Early disseminated: IV PCN or CTX for 28 days

  • Late disseminated: same as early localized but for 28 days

 

What constitutes early disseminated vs. late disseminated disease?

  • Early disseminated - Presents weeks to months after infection. It is the most common manifestation with a flu-like illness characterized by fevers, arthralgia, myalgia and lymphadenopathy and often associated with multiple concurrent EM eruptions at sites distant from the original tick attachment

  • Late disseminated - Occurs months or even years after infection. Characterized by arthritis (particularly in knee or point of infection), neurological deficits (numbness/tingling)

    • Late neurologic or skin findings (acrodermatitis chronica atrophicans and borrelial lymphomocytoma) are rare in the US but more frequent in european infections

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What are treatment options for COVID?

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What are common physical findings in endocarditis?

  • Janeway lesions, Osler nodes, Roth spots, splinter hemorrhages, petechiae, new murmur, new HF, FNS (septic emboli)

 

What are the Duke criteria?

  • Findings that help diagnose endocarditis with greater likelihood

  • Diagnose endocarditis if 2 major, 1 major and 3 minor, or five minor criteria met

  • Major: new valvular regurgitation, positive echocardiogram, positive blood cultures for endocarditis x2 or one positive culture for coxiella

  • Minor: fever, underlying heart condition or injection drug use, embolic vascular findings, immunologic phenomena, positive blood cultures not meeting major criteria

  • Duke Criteria for Infective Endocarditis - MDCalc

 

Initial imaging test?

  • TTE

  • Need TEE if endocarditis suspected and TTE nondiagnostic or if intracardiac device leads present 

 

Treatment of MRSA endocarditis? 

  • Vancomycin with a target AUC/MIC of 400-600 mg*hr/L or daptomycin if vanco MIC is high

 

Treatment of MRSA endocarditis of a prosthetic valve? 

 

Patients found to have strep bovis or clostridium septicum endocarditis should be evaluated for what?

  • Colon cancer

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What defines a fever of unknown origin?

  • Temp greater than 100.9 that remains undiagnosed for 3 days inpatient or 3 weeks outpatient 

 

What is the typical timeline for drug-induced fever?

  • Days to weeks after initiation of new drug but can occur at any time

 

What are the three most common causes of fevers? 

  • 1) Infection 2) Medication-related (ex. precedex) 3) Clot fever

 

What other causes to consider in a FUO?

  • Cancer, CTD, endocrine disorders, infections as below

 

What are health care associated causes?

  • Drug-induced, PE, occult abscesses, c. diff, sinusitis 

 

What are HIV associated causes?

  • TB, toxo, lymphoma, CMV, cryptococcosis

 

What are neutropenic causes?

  • Aspergillosis, candida, underlying malignancy

 

What is the initial approach to workup FUO?

  1. Obtain a complete history and physical and if positive perform appropriate and specific diagnostic testing

  2. Labs to order: CBC, electrolytes, LFT, blood cultures, U/A, Ucx,ESR, PPD skin test, CXR

  3. If further evaluation is required consider a CT of abdomen/pelvis with contrast

https://www.aafp.org/pubs/afp/issues/2003/1201/p2223.html

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What is HIV pre-exposure prophylaxis (PrEP)? 

  • Drug combo for high-risk individuals - tenofovir (TDF) and emtricitabine taken daily

 

How do you approach postexposure treatment?

  • Should be started within 72 hours of exposure

  • Should be with tenofovir, emtricitabine, and raltegravir or dolutegravir for 4 weeks

  • Test for HIV at exposure time, at 4 weeks, at 12 weeks, and at 4-6 moths 

 

What are neurologic disorders associated with HIV?

  • Progressive multifocal leukoencephalopathy = reactivation of JC virus - leads to unilateral or bilateral foci of demyelination

  • Central toxoplasmosis

  • Primary CNS lymphoma

  • Cryptococcal meningitis

 

What do patients need to be tested for prior to starting Abacavir?

  • HLAB5701 allele; increases risk for hypersensitivity reaction 

 

At what CD4 count is a patient at increased risk for cryptococcus, toxo, PJP, and MAC?

  • PJP: <200

  • Cryptococcus: <100

  • Toxo: <100

  • MAC: <50

 

What is the typical initial treatment regimen for HIV?

  • Three drugs from two different classes

  • Usually two NRTIs with an integrase inhibitor 

 

What is IRIS?

 

What are the typical CXR findings of PJP?

  • Diffuse bilateral interstitial infiltrates

  • PJP most common cause of PTX in patients with AIDS

 

How do you treat PJP?

  • 3 weeks of high dose Bactrim

  • Add glucocorticoids within 72 hrs if arterial PO2 <70 or A-a >35 mm

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What is used for PJP Prophylaxis?

 

What is the usual MAC ppx?

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When should you get a head CT prior to LP?

  • If there are signs/symptoms of increased intracranial pressure, hx of CNS disease, or new onset seizures

 

What are the two most common organisms causing bacterial meningitis?

  • Strep pneumo, neisseria meningitidis

 

What is the empiric antibiotic management for bacterial meningitis?

  • IV CTX and IV Vanc

  • Add ampicillin if age >50 or immunocompromised to cover Listeria

  • Dexamethasone should be given empirically in most cases with suspected bacterial meningitis and should be continued if strep pneumo is isolated

 

LP findings in HSV1 encephalitis? 

  • Lymphocytic pleocytosis (abnormal increase in lymphocytes), elevated protein, normal glucose (PCR of CSR if extremely sensitive and specific)

 

Where on imaging would you expect abnormalities in HSV encephalitis?

  • Temporal lobe

 

LP findings in tuberculous meningitis? 

  • Lymphocytic pleocytosis, elevated protein, low glucose

 

Tx for tuberculous meningitis? 

  • RIPE + dexamethasone

    • Rifampin, Isoniazid, Pyrazinamide, and Ethambutol

 

Most common cause of aseptic meningitis? 

  • HSV-2

 

How do you manage a brain abscess? 

  • Aspiration of brain abscess for culture to determine treatment, abx therapy for 4-8 weeks with follow-up cranial imaging

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What are the types of pneumonia?

  • Community-acquired PNA

  • Hospital-acquired PNA

  • Aspiration PNA

 

What is the CURB-65 criteria?

  • Helps determine which patients with pneumonia should be admitted

  • C=confusion, U=Urea > 20, R=Respiratory rate>30, B=BP <90/60, 65=Age >=65 (1 pt each)

  • 0-1 likely can be managed at home, 3-5 should be hospitalized, 2 admission vs close outpatient monitoring 

  • https://www.mdcalc.com/calc/324/curb-65-score-pneumonia-severity

 

What is the most common bacterial cause of CAP in all age groups?

  • Strep pneumo

 

What are the “atypical” bacteria?

  • Legionella, Mycoplasma pneumoniae (most common), Chlamydia pneumoniae, Chlamydia psittaci

 

What are the risk factors for MRSA and Pseudomonas infections?

  • MRSA- recent hospitalization with IV antibiotic use, recent flu-like illness, necrotizing or cavitary pneumonia, empyema, immunosuppression, ESRD, IVDU, contact sports, men who have sex with men

  • Pseudomonas- recent hospitalization with IV antibiotic use, frequent COPD exacerbations requiring glucocorticoid and/or antibiotic use, other structural lung disease (ie, bronchiectasis, cystic fibrosis), immunosuppression

 

Diarrhea and hyponatremia may be associated with which infection?

  • Legionella

 

Outpatient antibiotic options in a healthy patient?

  • Amoxicilin or doxy or macrolide

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Outpatient antibiotics options in patient with comorbidities?

  • Fluoroquinolone, or B-lactam plus macrolide or doxy

 

Inpatient, non-ICU antibiotics?

  • IV B-lactam plus macrolide or respiratory fluoroquinolone

 

Inpatient, ICU antibiotics?

  • IV B-lactam plus macrolide

 

Antibiotics for patient with risk factor for pseudomonas?

  • Antipseudomonal B-lactam plus macrolide or antipseudomonal quinolone

 

Antibiotics for patient with risk factor for MRSA?

  • Standard therapy plus Vanc

 

What is the role of MRSA nares testing in pneumonia?

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How do you define the stages of syphilis? 

  • Primary = painless chancre in genital or oral regions

  • Secondary = palm and sole rash, condyloma lata (plaque-like lesions in intertriginous areas)

  • Tertiary = stroke, AMS, auditory or ophthalmic abnormalities, Argyll Robertson pupil (don’t react but do accommodate)

  • Latent syphilis = secondary syphilis manifestations that resolve without treatment 

    • Early latent = less than 12 months 

    • Late Latent = greater than 12 months

 

How do you test for syphilis?

  • Automated enzyme immunoassay (EIA) followed by RPR or VDRL → if +EIA and next test is negative, then have second specific treponemal antibody test to confirm

 

How do you treat syphilis dependent on stage?

  • Primary or Secondary = Benzathine penicillin G IM x 1

  • Early latent = Benzathine penicillin G IM x 1

  • Late latent or syphilis of unknown duration = Benzathine penicillin G IM x 3

  • Neurosyphilis = Aqueous crystalline penicillin q4 or continuous infusion x 10-14 days

  • Pregnant patients = must get penicillin - may need desensitization if allergic

https://www.aafp.org/pubs/afp/issues/2003/0715/p283/jcr:content/root/aafp-article-primary-content-container/aafp_article_main_par/aafp_figure.enlarge.html

 

What infections/complications can chlamydia infection cause?

  • Urethritis, cervicitis, proctitis, epididymitis, PID (ectopic pregnancy, tubal infertility)

 

How do you treat chlamydia?

  • Azithromycin plus doxycycline

 

What underlying disorder should be tested for in recurrent disseminated gonococcal infection?

  • Terminal component complement deficiency 

 

How do you treat gonorrhea?

  • If chlamydia hasn’t been ruled out give CTX and oral doxy

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Define a UTI

  • Positive nitrite suggests gram negative bacteria that can convert nitrates to nitrites- E. coli, Klebsiella, Citrobacter, Proteus)

  • If negative, does not rule out infection. It may be that there is infection with non converting bacteria 

  • If both LE and nItrites positive→ highly predictive of underlying infection 

  • If both negative, high negative predictive value to rule out infection 

 

What are the only indications to treat asymptomatic bacteriuria (> 10^5 CFU/mL)?

  • Pregnancy 

  • Upcoming invasive urologic procedure 

  • 6 months after renal transplant (hotly debated)

 

What is a complicated UTI?

  • UTI in men, pregnant women, any foreign bodies (catheter or stones), immunocompromised, recent abx use (note - NOT age)

 

How to prevent CAUTIs?

  • Always order a UA with reflex hold urine culture, remove catheters as soon as you are able to

 

Management of a UTI

  • Uncomplicated UTI? Bactrim or nitrofurantoin (macrobid) 

  • Complicated UTI? Fluoroquinolone or Bactrim x 7-10 days 

  • Pregnant woman? Amox-clav, cefpodoxime, cefixime x 7 days 

  • Recurrent uncomplicated UTIs? Postcoital abx ppx or self-initiated therapy

  • Pyelo? Fluoroquinolone or 3rd gen cephalosporin or zosyn or carbapenem x 7-10 days all depending on severity

 

When should you obtain imaging for pyelonephritis?

  • Persistent fever > 72 hrs, persistent bacteremia, or worried about complications (abscess) - similar to pancreatitis

 

Should you get a repeat UA/Ucx after treatment?

  • Only in pregnant women

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Define Sepsis and Septic shock using Sepsis-3 Criteria:

  • Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection 

    • Organ dysfunction can be identified as an acute change in total SOFA score >/= 2 points consequent to the infection

  • Septic shock is a subset of sepsis in which underlying circulatory and cellular/metabolic abnormalities are profound enough to substantially increase mortality

    • Pts with septic shock can be identified with a clinical construct of sepsis with persisting hypotension requiring vasopressors ot maintain MAP >/= 65 mmHg and having a serum lactate level >2 mmol/L despite adequate volume resuscitation. 

 

What is the qSOFA score?

  • A qSOFA score is used as a prognostic measure of hospital mortality in patients at risk for sepsis

  • Although less robust than a SOFA score, does not require laboratory tests and can be assessed quickly and repeatedly. qSOFA criteria is more specific and can be used to prompt clinicians to further investigate for organ dysfunction, initiate/escalate therapy and consider referral to ICU

  • qSOFA score includes RR >/= 22min, Altered mentation and systolic blood pressure </= 100mmHg

  • For a qSOFA score <2, the full SOFA score should be used. While a score >/= 2 is suggestive of sepsis

 

What are the important steps in the evaluation of sepsis?

  • Cultures prior to antibiotics if possible

  • Consider sputum cx, paracentesis, thoracentesis, wound cx, LP, joint aspiration

  • UA hold for urine culture

  • Lactate

  • Imaging (x-ray, CT, or US of potential source)

 

What are the most important interventions in sepsis?

  • Fluid resuscitation with at least 30 mL/kg of IV balance crystalloid fluid within first 3 hours

  • Appropriate antibiotics within 1 hour of recognition (each hour of delay increases mortality 7%)

Surviving Sepsis 2021: https://journals.lww.com/ccmjournal/Fulltext/2021/11000/Surviving_Sepsis_Campaign__International.21.aspx

 

What is the utility of a MRSA nares? 

 

What are the SPICE organisms? 

  • Serratia, Providencia, “Indole-positive” Proteus (yes proteus vulgaris, not proteus mirabilis), Citrobacter, Enterobacter have inducible AmpC gene which means that they rapidly mutate to become resistant to beta-lactams even if they, at first, appear sensitive

  • Pseudomonas and Acinetobacter produce AmpC gene so they have intrinsic resistance and aren’t “inducible”

  • You can ONLY use 3rd gen cephalosporins for UTI/PNA requiring < 1 wk treatment

  • Otherwise, need to use non-cephalosporin antibiotics eg carbapenems, fluoroquinolones, aminoglycosides

  • Interestingly, cefepime and piperacillin/tazobactam may remain effective

 

Why does metabolic acidosis matter? 

  • Acidosis and low pH is associated with increased vasodilation, hypotension, and even arrhythmias. 

 

When should patients be started on bicarb-containing fluids?

  • Use bicarb-containing fluids in critically ill patients with pH < 7.2 and HCO3 < 20 PLUS AKI with Cr > 200% baseline

  • BICAR- ICU trial demonstrated mortality benefit if severe acidosis plus severe AKI (https://www.thelancet.com/article/S0140-6736(18)31080-8/fulltext)

  • Bicarb does NOT replace the need to correct the underlying cause of acidosis 

  • For patients with lactic acidosis, DKA, anion gap metabolic acidosis → primary treatment of the acidosis is treating the underlying cause. No benefit on survival or mortality by treating the number

 

Antibiotic guide- https://www.bugdrugdx.com/

Knowing which bugs ceftriaxone does NOT treat: https://twitter.com/sargsyanz/status/1572218511484719104

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How to interpret skin tests as positive?

  • >5 mm: HIV positive, recent contact with someone with active TB, fibrotic changes on CXR consistent with old TB, organ transplants, immunosuppressive conditions

  • >10 mm: injection drug users, arrival from high risk region in last 5 years, mycobacteriology lab employees, residents or employees in high risk congregate settings (health care facilities, jails, homeless shelters)

  • >15 mm: everyone else with no risk factors for TB

 

How is latent TB defined?

  • Positive skin test without any systemic manifestations of disease and a negative CXR

 

Gold standard for diagnosis of pulmonary TB?

  • Isolation of MTb from bodily fluid (sputum, BAL, pleural fluid) OR tissue cx (pleural or lung bx)

 

Treatment options for latent TB?

  • 4 months daily Rifampin

  • 3 months daily rifampin plus isoniazid

  • 3 months isoniazid plus rifapentine weekly

  • Can consider INH for 6-9 mos if contraindication to use of rifamycins

 

Treatment for active TB?

  • Isoniazid, rifampin, pyrazinamide, ethambutol daily for 2 months then isoniazid and rifampin daily for 4-7 months 

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What are some bacterial causes?

  • Salmonella, shigella, campylobacter, EHEC, ETEC, yersinia, vibrio

 

What are some viral causes?

  • Norovirus, rotavirus, adenovirus

 

What are some parasitic causes?

  • Giardia, cryptosporidium, amebiasis, cyclospora

 

When are antibiotics indicated in suspected bacterial etiologies?

  • Generally reserved for those who are sick enough to warrant admission with bloody diarrhea and/or hemodynamic instability 

  • Of note, one should be cautious if STEC is suspected as antibiotics can precipitate HUS

 

What empiric antibiotic regimen is appropriate? 

  • Azithro 1g x1 OR 500 mg daily x3d OR cipro 750 mg X1 OR 500 mg BID x3-5d OR levofloxaxin 500 mg x1 OR daily x 3-5d

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3042443/

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