8-Clinical Application Infectious Diseases

Name 4 mechanisms of antibiotic resistance.

Decreased penetration, altered target site, enzymatic inactivation, efflux pumps.

List the 5 types of beta-lactam resistance.

Penicillinase, Cephalosporinase, ESBL, AMP-C, Carbapenemase.

What does MIC stand for?

Minimum Inhibitory Concentration.

What does a lower MIC indicate?

Better effectiveness if the organism is susceptible.

What do the abbreviations S, R, and I mean in culture reports?

Susceptible, Resistant, Indeterminate.

Most specific sign of UTI on urinalysis?

Elevated WBC count.

What is pyuria defined as?

10 WBCs per high power field; ideally 50–100.

Why is leukocyte esterase not specific?

Detects small WBCs even in non-infectious cases.

What does a positive nitrite test suggest?

Presence of E. coli or Proteus, but not necessarily infection.

What 3 criteria are needed to diagnose UTI?

Symptoms, pyuria, >100K CFUs of true uropathogen.

When should asymptomatic bacteriuria be treated?

Always in pregnancy (reduces pyelo and preterm labor).

Why are blood cultures often contaminated?

Collected through skin or catheters.

How many blood cultures should be taken and from where?

Two, from different sites.

Why do blood cultures stay positive in endocarditis?

Because vegetations harbor bacteria despite antibiotics.

Which fungus can grow on normal culture medium?

Candida.

What indicates a high-quality sputum specimen?

High WBCs and low respiratory epithelial cells.

Best method for collecting a deep lung specimen?

Bronchial lavage.

When are stool cultures useful?

Only when targeting specific concerns like C. diff or parasites.

How is C. diff diagnosed?

PCR & Toxin + = Infection; PCR + & Toxin – = Clinical judgment.

How many specimens should be submitted for O&P testing?

Multiple samples.

Most common cause of UTI?

E. coli.

Name 3 other common UTI pathogens.

Klebsiella, Staph saprophyticus, Proteus mirabilis.

Name 3 main causes of community-acquired pneumonia.

Strep pneumo, H. influenzae, Moraxella catarrhalis.

Name 3 atypical causes of CAP.

Legionella, Mycoplasma, Chlamydophila.

Empiric treatment for community-acquired pneumonia?

Ceftriaxone + Azithromycin.

Most common cause of subacute endocarditis?

Strep viridans.

Most common cause of acute endocarditis?

Staph aureus.

Endocarditis from foreign body/prosthetic valve?

Staph epidermidis.

Name the HACEK organisms.

Haemophilus aphrophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella.

Most common bacteria in adult meningitis?

Strep pneumo, H. influenzae, Neisseria meningitidis, Listeria.

Which viral causes should always be considered in meningitis?

HSV, West Nile virus.

Empiric treatment for bacterial meningitis?

Ceftriaxone 2g BID + Vancomycin.

When should ampicillin be added to meningitis treatment?

Patients

When should IV acyclovir be added in meningitis?

If viral cause is suspected.

What defines neutropenic fever?

Fever ≥ 38.3°C + ANC <1500 (severe = <500).

Initial management of neutropenic fever?

Cultures, empiric Cefepime + Vancomycin, imaging.

What if neutropenic fever persists 4–7 days with no source?

Add antifungal agent.

HIV patient with pneumonia?

Pneumocystis jiroveci.

Alcoholic or diabetic with red currant jelly sputum?

Klebsiella.

Southwest desert exposure?

Coccidioidomycosis.

Exposure to rabbits?

Francisella tularensis.

Travel to Southeast Asia?

SARS.

Hispanic patient with seizure?

Neurocysticercosis (Taenia solium).

Bird exposure?

Chlamydia psittaci.

Bat exposure, caves, or bird droppings?

Histoplasma capsulatum.

Whooping cough or post-tussive vomiting?

Bordetella pertussis.

Contaminated water source?

Legionella.

Rose gardener?

Sporothrix.

Strep bovis bacteremia?

GI malignancy.

Recurrent pneumonia?

HIV, asplenia, lung cancer.

Recurrent meningitis?

HSV (Mollaret’s), CSF leak.

Necrotizing sinus infection?

Zygomycetes (Mucor, Rhizopus).

Sickle cell patient with osteomyelitis?

Salmonella.

Liver abscess with anchovy paste drainage?

Entamoeba histolytica.

Infection from Mexican soft cheese?

Listeria, Brucella.

Foul-smelling sputum?

Anaerobes, lung abscess.