Infectious Disease High-Yield Quizlet

Uncomplicated cystitis: first-line options

Nitrofurantoin, TMP-SMX, or fosfomycin; class notes also mention pivmecillinam.

Pyelonephritis: outpatient treatment in lecture

Ciprofloxacin in suitable patients; if unsuitable, an initial long-acting parenteral agent such as ceftriaxone followed by an appropriate oral agent guided by culture.

Suspected gonorrhea/chlamydia: empiric treatment

IM ceftriaxone plus oral doxycycline. Clinically, add doxycycline when chlamydia has not been excluded.

Suspected bacterial meningitis: empiric treatment

IV ceftriaxone plus IV vancomycin.

Meningitis with Listeria risk: additional antibiotic

Add IV ampicillin.

Suspected HSV encephalitis: treatment

IV acyclovir.

Early syphilis: preferred treatment

Benzathine penicillin G IM once for primary, secondary, or early latent syphilis.

Late latent syphilis or unknown duration: treatment

Benzathine penicillin G IM weekly for three doses.

Neurosyphilis: treatment

IV penicillin G for approximately two weeks.

Early Lyme disease: treatment

Oral doxycycline.

GAS pharyngitis: first-line treatment

Penicillin or amoxicillin.

Serious MRSA infection: treatment

IV vancomycin.

Suitable MRSA skin infection: oral options

Doxycycline or TMP-SMX; choice depends on syndrome and susceptibility.

Cryptococcal meningitis: treatment sequence

Amphotericin B plus flucytosine, followed by fluconazole.

Gram stain: information provided

Gram reaction, bacterial shape, and arrangement.

Culture: information provided

Organism growth and identification; permits antibiotic susceptibility testing.

Positive culture: interpretation trap

Growth can represent infection, contamination, or colonization; interpret with the clinical picture.

PCR/NAAT: what is detected?

Microbial genetic material. PCR is one type of NAAT.

Multiplex PCR: purpose

Tests for several pathogens simultaneously, useful for syndromes such as meningitis.

Antigen test: what is detected?

A pathogen component such as a protein, rather than the patient's antibodies.

Serology: what is detected?

The immune response, usually antibodies; early results may be negative during the window period.

Acid-fast stain: important organisms

Mycobacteria, especially tuberculosis and MAC, with lipid-rich cell walls.

Cultures and urgent antibiotics: sequence

Obtain cultures before antibiotics when feasible, but do not delay urgent treatment in an unstable patient.

Prophylactic antimicrobial therapy

Treatment to prevent infection.

Empiric antimicrobial therapy

Treatment targeting likely organisms before microbiologic confirmation.

Definitive antimicrobial therapy

Treatment tailored to identified organisms and susceptibility results.

Gram-positive bacteria: structure and stain

Purple on Gram stain; thick peptidoglycan layer.

Gram-negative bacteria: structure and stain

Pink on Gram stain; thin peptidoglycan plus an outer membrane.

Gram-negative bacteria: inflammatory component

Outer-membrane lipopolysaccharide (LPS) can provoke a strong inflammatory response.

Vancomycin: spectrum

Gram-positive coverage; does not cover gram-negative bacteria.

Mycoplasma: why routine Gram stain is unhelpful

It lacks a cell wall.

Treponema pallidum: why routine Gram stain is unhelpful

It is too thin to visualize reliably with routine Gram staining.

Mycobacteria: identification

Use acid-fast staining because of the lipid-rich cell wall.

Chlamydia/Rickettsia: routine Gram-stain limitation

Small intracellular organisms are poorly identified with routine Gram staining.

Legionella: Gram-stain limitation

It stains poorly with routine Gram staining.

Amoxicillin: mechanism

Interferes with bacterial cell-wall synthesis.

Azithromycin: mechanism and role

Inhibits bacterial protein synthesis and adds coverage for atypical bacteria.

Amoxicillin plus azithromycin: rationale

Provides typical and atypical bacterial coverage in selected respiratory infections; not automatically needed for every infection.

Fungi: basic identification

Eukaryotic organisms; can appear as yeast or mold.

Yeast versus mold: examples

Candida and Cryptococcus are yeasts; Aspergillus is a mold.

E. coli: identification and common infections

Gram-negative rod; normal gut flora; common cause of UTIs and some diarrheal illnesses.

Pseudomonas: identification clues

Gram-negative rod with blue-green pigment; associated with devices, burns, ventilators, and cystic fibrosis.

Pseudomonas: treatment options

Antipseudomonal agents such as cefepime, piperacillin-based therapy, or appropriate carbapenems; susceptibility matters.

S. aureus: Gram-stain appearance

Gram-positive cocci in clusters.

S. aureus: common infections

Abscess, bacteremia, endocarditis, osteomyelitis, and septic arthritis.

Staphylococcal abscess: source control

Incision and drainage, with culture; antibiotics depend on complications and clinical context.

Staphylococcal biofilm: source control

Remove infected equipment when indicated; antibiotics alone may not control the source.

MRSA: resistance gene/testing

mecA-associated altered binding protein; PCR can identify the resistance gene.

Streptococcus: Gram-stain appearance

Gram-positive cocci in chains or pairs.

Scarlet fever: recognition

Sandpaper-textured rash and strawberry tongue associated with GAS.

Acute rheumatic fever: recognition

Weeks after GAS pharyngitis: large-joint arthritis, carditis, and possible subcutaneous nodules.

Infective endocarditis: clues and diagnosis

Fever, new murmur, bacteremia, and septic emboli; evaluate with blood cultures and echocardiography.

Infective endocarditis: treatment approach

Prolonged antibiotics, initially IV.

Hemolytic uremic syndrome: classic triad

Hemolytic anemia, thrombocytopenia, and acute kidney injury, often after Shiga toxin-associated diarrhea.

Daptomycin: why not pneumonia?

Pulmonary surfactant inactivates it.

C. difficile: organism type

Anaerobic, spore-forming bacillus.

C. difficile: clinical clues

Recent antibiotics or hospitalization, at least three unformed stools in 24 hours, abdominal pain, and possible fever/leukocytosis.

C. difficile: testing approach

Sensitive PCR/GDH screening with toxin testing helps distinguish infection from carriage; test symptomatic patients.

C. difficile: preferred nonfulminant treatment

Fidaxomicin 200 mg orally twice daily for 10 days.

C. difficile: oral vancomycin alternative

Vancomycin 125 mg orally four times daily for 10 days.

Fulminant C. difficile: treatment

Vancomycin 500 mg PO/NG four times daily plus IV metronidazole; consider rectal vancomycin with ileus.

C. difficile notes correction: severe versus fulminant

The high-dose vancomycin plus IV metronidazole regimen is for fulminant disease, such as shock, ileus, or megacolon; high WBC alone does not establish this category.

Oral versus IV vancomycin

Oral vancomycin stays mainly in the gut and treats C. difficile; IV vancomycin treats systemic gram-positive infections.

C. difficile: hand hygiene

Soap and water physically remove spores; alcohol hand sanitizer is not reliable against spores.

Cystitis: distinguishing findings

Dysuria, urgency, frequency, and bladder discomfort without typical fever or flank pain.

Pyelonephritis: distinguishing findings

Fever/systemic illness and flank pain, with possible dysuria, nausea, and vomiting.

Pyelonephritis: diagnostic priority

Always obtain a urine culture.

Dysuria with genital discharge: consider what?

Urethritis/STI; use site-appropriate NAAT rather than assuming simple cystitis.

Nitrofurantoin: site limitation

Useful for bladder infection, not pyelonephritis; notes emphasize poor prostate penetration.

Asymptomatic bacteriuria: treatment principle

A positive culture alone does not mean treat; pregnancy and certain urologic procedures are important exceptions.

Primary syphilis: classic lesion

Painless chancre at the site of inoculation.

Secondary syphilis: manifestations

Rash, condyloma lata, patchy alopecia, and lymphadenopathy.

Latent syphilis: manifestations

No symptoms; diagnosed with serology and history/staging.

Neurosyphilis: manifestations and testing

Neurologic changes or cranial nerve dysfunction; CSF evaluation including VDRL.

Syphilis: diagnostic approach

Treponemal plus nontreponemal antibody testing.

Syphilis: window-period trap

Antibodies may be undetectable early; a negative early test does not completely exclude infection.

Syphilis: monitor treatment response

Follow RPR/VDRL titers; a fourfold decline is meaningful. Titers do not have to reach zero.

Syphilis: example of fourfold titer decline

1:32 to 1:8.

Genital HSV: lesion and preferred test

Painful vesicles/ulcers; fresh-lesion PCR/NAAT.

Genital HSV: treatment options

Oral acyclovir, valacyclovir, or famciclovir; daily suppressive therapy may reduce recurrence.

HSV genital versus CNS disease: route

Genital disease generally uses oral antiviral therapy; HSV CNS disease uses IV acyclovir.

Chancroid: organism, lesion, treatment

Haemophilus ducreyi; painful ulcer; azithromycin or ceftriaxone.

Chlamydia: presentation and diagnosis

Often asymptomatic; can cause urethritis/cervicitis; diagnose with site-specific NAAT.

Chlamydia: preferred regimen in chart

Doxycycline 100 mg orally twice daily for seven days.

Gonorrhea: identification, testing, treatment

Gram-negative cocci; NAAT, culture when needed; IM ceftriaxone.

STI prevention and reinfection reduction

Condoms reduce risk; partner evaluation and treatment help prevent reinfection.

Lyme disease: organism and vector

Borrelia burgdorferi, a spirochete, transmitted by infected Ixodes ticks.

Lyme versus syphilis: shared organism shape

Both causative organisms are spirochetes.

Early localized Lyme: manifestation

Erythema migrans, which need not look like a perfect bull's-eye.

Disseminated/late Lyme: important manifestations

Neurologic involvement, carditis/heart block, and large-joint arthritis.

Lyme disease: testing in chart

Two-tier antibody testing: EIA/IFA followed by confirmatory Western blot.

Lyme disease: window-period trap

Early antibody testing can be falsely negative, especially with erythema migrans; sensitivity improves after several weeks.

Lyme antibodies after treatment

Can persist after successful treatment; positive antibodies do not necessarily indicate active infection.

Lyme with significant neurologic/cardiac disease

May require IV therapy such as ceftriaxone, depending on manifestation and severity.

Lyme prophylaxis emphasized in lecture

Selected high-risk tick bites: doxycycline 200 mg once within 72 hours of tick removal; not for every tick bite.

Lyme prevention

Avoid tick exposure, use protective clothing, perform tick checks, and remove ticks promptly.

RMSF: recognition and treatment

Rash begins at wrists/ankles and spreads inward, often involving palms/soles; start doxycycline promptly when suspected.

Meningitis: location and manifestations

Inflammation of meninges; fever, headache, neck stiffness, and photophobia.

Encephalitis: location and manifestations

Inflammation of brain tissue; confusion, seizures, and focal deficits.

Myelitis: location and manifestations

Spinal cord inflammation; weakness, sensory level, and autonomic dysfunction.