NAPLEX 2026 - ID2: Bacterial Infections

What are common causes (bugs) of infection from surgery?

Skin flora: staph and strep

Gram-negative and anaerobes play a role in select surgeries (intra-abdominal procedures)

Describe the timing of perioperative antibiotics

Pre-op: infuse antibiotic (cefazolin or cefuroxime) within 60 minutes before first incision

- if quinolone or vanco is used, start 120 minutes before first incision

Intra-op: additional doses may be considered for longer surgeries (> 4h) or if there is major blood loss

Post-op: antibiotics are not usually needed; if used, d/c within 24h

What antibiotic is used in most surgeries? What's an alternative? When is additional coverage needed?

Cefazolin (1st gen) or cefuroxime (2nd gen) to prevent MSSA and strep

Clindamycin (or vanco) if patient has a beta-lactam allergy

Additional Coverage:

- GI surgeries needs to cover skin flora + broad gram-negative and anaerobic organisms

- add vanco if MRSA colonization or risk present

What is the recommended antibiotic regimen for GI surgeries?

Cefazolin

+

either metronidazole, cefotetan, cefoxitin, or Unasyn

What are the classic symptoms of meningitis?

Fever

Headache

Nuchal rigidity (stiff neck)

Altered mental status

(Others include chills, vomiting, seizures, rash, and photophobia)

How is diagnosis of meningitis made?

Lumbar puncture during which a sample of cerebrospinal fluid CSF is collected

High CSF pressure detected during LP is another sign of possible infection

What are the most common bacterial causes of meningitis?

Neisseria meningitidis

Streptococcus pneumoniae

Haemophilus influenzae

Risk of Listeria monocyte genes is higher in neonates, patients age > 50, and immunocompromised patients

How long should you treat bacterial meningitis?

Dependent on pathogen

7 days for N. meningitidis and H. influenzae

10-14 days for S. pneumoniae

At least 21 days for Listeria monocyogenes

What is their empiric treatment for bacteria meningitis?

Age <1 month (neonates):

Ampicillin (for Listeria coverage)

+ ceftazidime or cefepime

+/- gentamicin

Age 1 month - 50 years:

Ceftriaxone

+ vancomycin (double S.pneumoniae coverage)

Age > 50 or immunocompromised:

Ampicillin (for Listeria coverage)

+ ceftriaxone

+ vancomycin (double S.pneumoniae coverage)

What can be added to antibiotic treatment to prevent neurological complications and death from pneumococcal meningitis ?

IV dexamethasone, administered 15-20 minutes prior to or with first antibiotic dose

Administer in all cases since causative pathogen is not known at the time of empiric treatment

Signs and symptoms of acute otitis media (AOM)?

Often gave rapid onset and include:

- bulging tympanic membrane (eardrum)

- otorrhea (middle ear fluid)

- otalgia (ear pain)

- fever

- crying

- tugging or rubbing of the ears

What are common bugs associated with AOM?

S. pneumoniae

H. influenzae

Moraxella catarrhalis

When can you consider observation (without antibiotics) for AOM in kids?

Observe for 2-3 days if symptoms are non-severe (otalgia < 48h, no otorrhea, temperature < 102.2°F) and:

- age 6-23 months: symptoms in one ear only

- age >/2 years: symptoms in one or both ears

If symptoms do not improve or worsen, use antibiotics

What are the 1st line treatment options for AOM (with doses)? Alternatives?

1st line: Amoxicillin or Augmentin

- 90 mg/kg/day in 2 divided doses

- w/ Augmentin, use formulation with the least amount of clavulanate to decrease risk of diarrhea (Augmentin ES-600)

Alternatives if non-severe penicillin allergy: 2nd or 3rd gen cephalosporins

- cefdinir, cefuroxime, cefpodoxime, ceftriaxone

Treatment failure (not improved after 2-3 days):

- ceftriaxone IM x 3 days

What is the treatment duration with oral medication for AOM?

10 days for age < 2

7 days for ages 2-5

5-7 days for ages >/= 6

What are the clinical presentation and treatment options for common cold?

Clinical presentation: sneezing, runny nose, mild sore throat and/or cough, congestion

Treatment:

- no antibiotics (viral); resolves in a few days

- symptomatic care w OTCs

What's the clinical presentation, criteria for anti-infective treatment, and treatment options for influenza?

Clinical presentation: sudden fever, chills, fatigue, myalgia, dry cough, sore throat, HA (symptoms more severe than common cold)

Criteria: suspected or confirmed infection (positive rapid antigen test) and:

- symptoms < 48h

- severe illness

- or symptoms + risk factors

Treatment: symptomatic care w/ or w/out antiviral

What's the clinical presentation, criteria for anti-infective treatment, and treatment options for COVID-19?

Clinical presentation: can range from asymptomatic to severe symptoms (fever, chills, SOB, myalgia, loss of taste/smell, cough)

Criteria: suspected or confirmed infection (positive rapid antigen test) and:

- immunocompromised

- older age

- or at risk for progression to severe disease (chronic lung disease)

Treatment: symptomatic care w/ or w/out antiviral

What's the clinical presentation, criteria for anti-infective treatment, and treatment options for pharyngitis (strep throat)?

Clinical presentation: sore throat, fever, swolllen lymph nodes, white patches (exudates) on tonsils

- absence of cough, runny nose, and congestion

Criteria: rapid antigen test (tonsil swab) or throat culture positive for S. pyogenes

Treatment: penicillin or amoxicillin

- mild allergy: 1st or 2nd gen cephalosporin

- severe allergy: macrolide (azithromycin or clindamycin)

What are common bugs that cause acute sinusitis?

S. pneumoniae

H. influenzae

M. catarrhalis

What's the clinical presentation, criteria for anti-infective treatment, and treatment options for acute sinusitis?

Clinical presentation: nasal congestion, purulent nasal discharge, facial/ear/dental pain or pressure, HA, fever

Criteria:

- >/= 10 days of persistent symptoms or

- >/= 3 days of severe symptoms (temp > 102) or

- worsening symptoms after initial improvement

Treatment: Augmentin or

- symptomatic care for up to 7 days - antibiotics can be used if symptoms worsen or do not improve

What are the key defining features of acute bronchitis?

Non-productive or productive cough lasting 1-3 weeks

Often preceded by an upper respiratory tract virus

Diagnosis made by ruling out other causes of acute cough - chest x-ray finding are typically normal

Antibiotics not recommended - supportive care W

What is pertussis and how do you treat it?

Acute bronchitis caused by Bordetella pertussis (whooping cough)

- forceful coughs followed by an inspiratory "whoop" sound

Highly contagious - treat with macrolides

- azithromycin, clarithromycin

What is a COPD exacerbation defined as and what are the three cardinal symptoms?

Increase in symptoms that worsen over < 14 days

Cardinal symptoms:

- increased dyspnea

- increased sputum volume

- increased sputum purulence

What are bacterial triggers of a COPD exacerbation?

H. influenzae

M. catarrhalis

S. pneumoniae

How do you manage an acute COPD exacerbation?

Supportive treatment (oxygen, short-acting bronchodilators, steroids)

Antibiotics for 5-7 days if any one of the following:

- all 3 cardinal symptoms

- increases sputum purulence + 1 additional symptom

- mechanically ventilated

Preferred antibiotics:

- Augmentin

- azithromycin

- doxycycline

- respiratory quinolone

What is community-acquired pneumonia (CAP) typically caused by?

S. pneumoniae

H. influenzae

Atypical pathogens - Mycoplasma pneumoniae, Chlamydophila pneumoniae

What are common symptoms of pneumonia?

SOB

Fever

Cough with purulent sputum

Pleuritic chest pain

Rales (crackling noises in the lungs)

Tachypnea (increase RR)

Decreased breath sounds

What is the gold standard diagnostic test for pneumonia?

Chest x-ray

Will have infiltrates, opacities, or consolidations to indicate pneumonia

What is the typical duration of treatment for CAP?

5-7 days

Outpatient CAP treatment?

Look for comorbidities (chronic heat, lung, liver, or renal disease; diabetes; alcohol use disorder; malignancy; or asplenia)

Healthy (no comorbidities):

- amoxicillin high dose or

- doxycycline or

- macrolide if local pneumococcal resistance < 25%

High risk (comorbidities):

- beta-lactam (Augmentin or cephalosporin) + macrolide or doxycycline or

- respiratory quinolone monotherapy

Inpatient CAP treatment?

Non-severe (admission to a gen med unit):

- beta lactam (ceftriaxone or Unasyn) + macrolide or doxycycline or

- respiratory quinolone monotherapy

Severe (admission to ICU):

- beta lactam + macrolide

- beta lactam + respiratory quinolone (no monotherapy)

Risk factors for pseudomonas and/or MRSA:

- MRSA (prior resp isolate or positive nasal swab): add vanco or linezolid

- pseudomonas (prior resp isolate): use beta-lactam active against it such as Zosyn, cefepime, or meropenem

- hospitalization and use of parental antibiotics in past 90 days: cover both MRSA and pseudomonas

When do HAP and VAP occur? What are the common pathogens?

HAP onset > 48h after hospital admission

VAP occurs > 48h after the start of mechanical ventilation

Common pathogens:

- nosocomial: risk for MRSA and MDR gram negative rods (pseudomonas, acinetobacter, enterobacter, E.coli, klebsiella) is increased

How do you select an empiric regimen for HAP/VAP?

All patients need antibiotic for pseudomonas and MSSA:

- cefepime, Zosyn, levofloxacin

Add vanco or linezolid if risk for MRSA

- cefepime + vanco

- meropenem + linezolid

- aztreonam + vanco

Use 2 antibiotics for pseudomonas if risk for MDR gram negative pathogens

- Zosyn + cipro + vanco

- cefepime + gentamicin + linezolid

Abx that covers pseudomonas:

- beta-lactams (Zosyn, cefepime, ceftazidime, imipenem/cilastatin, meropenem)

- levofloxacin, ciprofloxacin

- aztreonam

- aminoglycosides

What is tuberculosis (TB) caused by?

Mycobacterium tuberculosis (MTB)

(Aerobic, non-spore forming bacillus)

Latent TB vs active TB symptoms

Latent: immune system contains infection and patient lacks symptoms

Active:

- transmitted by aerosolized droplets and is highly contagious

- cough, hemoptysis (coughing up blood), purulent sputum, fever, night sweats, weight loss

How do you diagnose latent TB?

Tuberculin skin test (TST) (aka PPD test)

- solution injected intradermally and skin is inspected for induration 48-72h later

Or

Interferon-gamma release assay (IGRA) blood test

- preferred in patients with hx of bacille Calmette-Guerin (BCG) vaccine because a false positive TST can occur

Criteria for positive TB skin test results

>/ 5 mm:

- close contacts of recent active TB cases

- HIV infection

- immunosuppression

>/= 10 mm:

- immigrants from high burden countries

- clinical risk (IV drug use, diabetes)

- residents/employees of "high risk" congregate setting (prisons, healthcare facilities, homeless shelters)

>/= 15 mm:

- no risk factors

What are the preferred treatment regimens for latent TB?

INH and rifapentine once weekly for 12 weeks via directly observed therapy (DOT)

- do not use this regimen if pregnant

INH with rifampin daily x 3 months

Rifampin daily x 4 months

INH for 6-9 months

- may be preferred in HIV positive patients taking ART

How do you diagnose active TB?

Positive TST or IGRA confirmed with chest x-ray showing a consolidation or cavitation (empty space)

MTB is an acid-fast bacilli (AFB) - it can be detected with an AFB smear of sputum but test in non-specific - definite diagnosis must be made via sputum culture or PCR

- slow growing - culture may take up to 6 weeks

What is the preferred treatment regimens for active TB?

Intensive phase:

- 4 drugs for 2 months

- RIPE: rifampin + isoniazid + pyrazinamide + ethambutol

Continuation phase:

- 2 drugs for 4 months

- isoniazid and rifampin

6 months total treatment duration

Rifampin side effects

Increases LFTS

Hemolytic anemia (positive Coombs test)

Flu-like syndrome

Orange-red discoloration of body secretions (saliva, urine, sweat, tears) - can stain contact lenses and clothing

Rifampin drug interactions

Potent inducer of CYP450 (1A2, 2C8, 2C9, 2C29, 3A4) and P-gp - it can significantly decrease the concentrations of:

- protease inhibitors (CI - substitute rifabutin)

- warfarin (very large decrease in INR)

- oral contraceptives (decreases efficacy)

Do not use with apixaban, rivaroxaban, edoxaban, or dabigatran

Isoniazid boxed warning

Serve and fatal hepatitis

Isoniazid warnings

Peripheral neuropathy

How do you decrease risk of developing peripheral neuropathy when taking isoniazid?

Pyridoxine (vitamin B6) 25-50 my daily

Isoniazid side effects

Increased LFTs

DILE

hemolytic anemia (positive Coombs test)

Pyrazinamide contraindications

Acute gout

Severe hepatic damage

Pyrazinamide side effects

Increase LFTs

Hyperuricemia/gout

Ethambutol contraindications

Optic neuritis; do not use in young children, unconscious patients, or anyone who cannot report visual changes

Ethambutol side effects

Increased LFTs

Optic neuritis (dose related) - requires baseline and monthly vision exams

Confusion

Hallucinations

How is infective endocarditis diagnosed?

Modified Duke Criteria: echo to visualize the vegetation and positive blood cultures

What are most common species of organisms associated with infective endocarditis?

Staph, Strep, and Enterococcus

What's the typical duration of treatment for infective endocarditis?

4-6 weeks of IV antibiotic treatment

What's the preferred treatment for endocarditis for each possible pathogen?

Strep: penicillin or ceftriaxone (+/- gentamicin)

MSSA: nafcillin or cefazolin (+ gentamicin and rifampin if prosthetic valve)

MRSA: vancomycin ( + gentamicin and rifampin if prosthetic valve)

Enterococci: penicillin or ampicillin + gentamicin

Or ampicillin + high-dose ceftriaxone

What patients are at high risk for infective endocarditis at the dentist?

Dental work needed, such as root canal (not routine cleaning)

+

Select cardiac condition, including:

- prosthetic heart valve or heart valve repaired with artificial material

- history of endocarditis

- heart transplant with abnormal heart valve function

- certain congenital heart defects, including heart/heart valve disease

What's the recommended infective endocarditis adult dental prophylaxis regimen?

Administer one dose 30-60 minutes before procedure

1st line: amoxicillin 2g

- if allergic: azithromycin or Clarithromycin 500mg or doxycycline 100 mg

What is spontaneous bacterial peritonitis?

Infection if the peritoneal space that often occurs in patients with cirrhosis or ascites

Infection suspected if ascitic fluid (collected via paracentesis) reveals >/= 250 cell/mm3 PMNs (polymorphonuclear leukocytes)

What's the treatment plan for someone with SBP?

Empiric treatment with ceftriaxone for 5-7 days to target likely pathogens (strep, proteus, E.coli, klebsiella)

- carbapenem may be used in critically ill patients or those at risk for MDRs

Secondary prophylaxis with Bactrim (or ciprofloxacin)

What pathogens should empiric antibiotic treatment for intra-abdominal infections cover?

Polymicrobial!

- strep

- enteric gram-negatives

- anaerobes (B. fragilis)

If risk of MDR (critically ill, hospitalized > 48h, abx in past 90 days), cover pseudomonas and other resistant organisms

What are possible treatment options for community acquired intra-abdominal infections?

Cover PEK, anaerobes, strep:

- ertapenem

- moxifloxacin

- (cefuroxime or ceftriaxone) + metronidazole

- (ciprofloxacin or levofloxacin) + metronidazole

What are possible treatment options for risk of resistant/nosocomial pathogens in intra-abdominal infections?

Cover PEK, pseudomonas, enterobacter, anaerobes, strep, +/- enterococci:

- carbapenem (except ertapenem)

- Zosyn

- (cefepime or ceftazidime) + metronidazole

What are the treatment options for impetigo?

Use warm, wet compress to remove dried crusts

Limited, localized lesions:

- topical antibiotic, usually mupirocin

Numerous, extensive lesions:

- cephalexin

- dicloxacillin

What are the treatment options for folliculitis/furuncle/carbuncle?

Use an antibiotic that covers MSSA and MRSA:

- Bactrim

- doxycycline

What's the treatment for mild and severe cellulitis?

Mild: antibiotic must cover strep and MSSA (treat 5 days)

- cephalexin

- dicloxacillin

- beta-lactam allergy: clindamycin

Severe: needs MRSA coverage (IV) (treat 7-14 days)

- vancomycin

- daptomycin

- linezolid

- others: ceftaroline, tedizolid, telavancin

What's the treatment options for mild and severe abscesses?

Mild: cover MSSA and MRSA

- Bactrim

- doxycycline

- others: Minocycline, clindamycin, linezolid

Severe: MRSA (IV)

- vancomycin

- daptomycin

- linezolid

What are the treatment options for necrotizing fasciitis?

Urgent surgical debridement

Empiric therapy is broad:

- vancomycin or daptomycin + beta-lactam (Zosyn, meropenem) + clindamycin

A urinalysis can aid in the diagnosis of UTI and is considered positive when?

Pyuria (WBC > 10)

Bacteria

Positive leukocyte esterase and/or nitrates

Presence of bacteria alone does not indicate UTI and does not require treatment except when?

Asymptomatic bacteriuria in pregnancy

What are the symptoms of cystitis and pylenephritis ?

Cystitis:

- urgency and frequency (including nocturia)

- dysuria (painful/burning urination)

- suprapubic tenderness

- hematuria

Pyelonephritis:

- flank/CVA pain

- abdominal pain, N/V

- fevers, chills, malaise

What are the drugs of choice for acute cystitis?

Nitrofurantoin (Macrobid) 100 mg PO BID x 5 days

(CI if CrCl: < 60)

Bactrim DS 1 tablet PO BID x 3 days

(Do not use if sulfa allergy or >20% E.coli resistance rate)

Fosfomycin 3g PO x 1 dose

What are the treatment options for acute pyelonephritis?

Moderately ill outpatient (PO)

if local quinolone resistant 10%:

- ceftriaxone 5-7 days

Severely ill hospitalized patient (IV)

- initial: ceftriaxone or quinolone

- concern for resistance (Zosyn, carbapenem (if ESBL producing organism suspected)

What medication can help with dysuria from UTIs but does not treat the infection? What are important counseling points?

Phenazopyridine (Pyridium, Azo)

- 2 days max duration

- Take with 8oz of water and with food to minimize stomach upset

- Can cause red-orange coloring if the urine and other body fluids

What's the preferred treatment options for UTI in pregnancy?

Beta-lactams: amoxicillin +/- clavulanate or an oral cephalosporin (cephalexin)

If allergy: Nitrofurantoin or Bactrim

Avoid quinolones due to cartilage toxicity

What are symptoms and risk factors for a C.diff infection?

Symptoms: at least 3 watery stools per day, abdominal cramps, fever, and elevated WBC

Risk factors:

- recent healthcare exposure

- use of PPIs

- advanced age

- immunocompromised state

- obesity

- previous CDI

What are the treatment options for CDI?

1st episode - tx for 10 days with:

- fidaxomicin

- vancomycin

2nd episode - tx for 10 days with:

- fidaxomicin

- vancomycin standard regimen followed by prolonged tapered course

3rd episode:

- fidaxomicin x 10 days

- vancomycin standard regimen followed by prolonged tapered course or

- vancomycin standard regimen followed by rifaxamin x 20 days

- fecal microbiota transplantation

What's the treatment for syphilis (primary, secondary or early latent and late latent or tertiary)?

Primary, secondary, early latent:

- penicillin G benzathine (Bicillin L-A) 2.4 million units IM x 1 dose

- allergy: doxycycline x 14 days (if pregnant - desensitize and treat with Bicillin L-A

Late latent or tertiary:

- penicillin G benzathine (Bicillin L-A) 2.4 million units IM weekly x 3 weeks

- allergy: doxycycline x 28 days

What's the treatment for neurosyphilis?

Penicillin G aqueous (IV)

What's the treatment for gonorrhea?

Ceftriaxone 500 mg IM x 1 (if <150 kg)

(If chlamydia has not been excluded: add doxycycline)

What's the treatment for chlamydia?

Non-pregnant: doxycycline 100 mg PO BID x 7 days

Pregnant: azithromycin 1 g PO once

What's the treatment for bacterial vaginosis?

Metronidazole (tablet or gel)

What's the treatment for trichomoniasis?

Metronidazole (even if pregnant)

What's the treatment for genital warts?

Imiquimod cream (tx not required if asymptomatic - generally resolves spontaneously)

Vaccine available to decrease risk of general warts and cervical and other cancers (HPV): Gardasil

What patients require penicillin desensitization for treatment of syphilis and what's the process?

Pregnant patients (doxycycline AEs in fetus)

Patients with poor adherence/follow-up

1. Confirm allergic reaction with skin test

2. Temporarily desensitize patient with approved protocol

3. Treat with IM penicillin G benzathine

What are the symptoms of Rocky Mountain spotted fever?

Fever, headache, muscle pain

Followed 3-5 days later by an erythematous petechial rash

What's the drug of choice for treating Rocky Mountain spotted fever and Lyme disease?

Doxycycline