BACTERIAL SKIN INFECTIONS
A 28-year-old presents to urgent care with localized erythema, warmth, and pain of the forearm after a small cut. No systemic symptoms, no healthcare exposure, no prior MRSA history. What is the most appropriate first-line oral antibiotic choice and why?
CEPHALEXIN PO. THIS IS UNCOMPLCATED CELLULITIS WITH A LOW RISK FOR MRSA. AND CELLULITIS IS CASUED BY STREP OR MSSA, SO WE NEED AN RX THAT CAN COVER BOTH.
CEPHALEXIN IS 1ST GEN CEPHALOSPORIN AND IT HAS MILDER ADRs, AND IT COVERS FOR STREP AND STAPH. ITS ALSO THE FIRST LINE RX FOR SIMPLE CELLULITIS.
A child presents with fever and tender regional lymphadenopathy one week after being scratched by a cat. What is the diagnosis and first-line treatment?
cat scratch disease caused by Bartonella henselae, and first-line treatment is a macrolide - azithromycin
A 54-year-old presents with rapidly spreading erythema of the leg, severe pain out of proportion to physical exam, fever, hypotension, and systemic toxicity after a minor skin abrasion. The area is becoming dusky with black and discolored skin. What is the diagnosis and the most critical next step in management?
This is necrotizing fasciitis, most commonly caused by Group A Streptococcus or mixed organisms, and the most critical next step is immediate surgical debridement plus broad-spectrum IV antibiotics, because antibiotics alone are insufficient and delayed surgery is associated with extremely high mortality.
A teenager is diagnosed with streptococcal pharyngitis and started on amoxicillin. When is it safe for them to return to school or work?
The patient may return 24 hours after the first dose of antibiotics, because treatment rapidly reduces infectivity and transmission risk.
A pregnant patient presents with flu-like symptoms and lymphadenopathy after cleaning a litter box daily. You suspect toxoplasmosis. What is the appropriate treatment and why is this infection clinically important in this population?
This is toxoplasmosis caused by Toxoplasma gondii, and treatment is pyrimethamine + sulfadiazine with leucovorin, because this organism can cause congenital infection with severe fetal complications, making early identification and treatment critical.
A patient presents with chronic abdominal discomfort, diarrhea, weight loss, and reports frequent consumption of undercooked beef and pork while traveling. Stool studies reveal parasitic ova. Based on this exposure and presentation, what is the most likely class of organism and the appropriate treatment?
This presentation is most consistent with a cestode infection, aka tapeworm, and treatment is praziquantel, because parasites acquired from undercooked beef and pork cause intestinal helminth infections.
A sexually active woman presents with frothy, yellow-green vaginal discharge, vaginal irritation, and a “strawberry cervix” on exam. What is the diagnosis and first-line treatment?
This is Trichomonas vaginalis, and first-line treatment is metronidazole, because Trichomonas is a flagellated protozoan.
A newly diagnosed HIV patient with no prior treatment presents for initiation of antiretroviral therapy. What is the recommended structure of a first-line regimen and give an example of a medication.
First-line HIV treatment consists of one integrase strand transfer inhibitor (INSTI) plus two nucleoside reverse transcriptase inhibitors (NRTIs), because this combination provides potent viral suppression, high barrier to resistance, and good tolerability.
biktarvy, triumeq
An immunocompromised patient presents with cough and shortness of breath. Imaging shows pulmonary nodules, and fungal cultures grow encapsulated yeast. What is the diagnosis and treatment?
This is pulmonary cryptococcosis, and treatment is fluconazole, because Cryptococcus neoformans commonly causes lung infection in immunocompromised patients.
A hospitalized patient with rapidly spreading cellulitis has fever, leukocytosis, and a prior history of MRSA. What empiric IV antibiotic should be started immediately and why?
Vancomycin, because severe infection with MRSA risk requires IV MRSA coverage.
A 22-year-old man presents with a swollen, painful knuckle after punching someone in the mouth, now with decreased range of motion and purulent drainage. What is the best management?
This is an infected human bite wound (“fight bite”), and treatment is ampicillin/sulbactam because human oral flora is polymicrobial and requires broad gram-positive, gram-negative, and anaerobic coverage.
A diabetic patient presents with chronic foot pain, swelling, and fever, and imaging suggests bone involvement. Blood cultures are pending. What is the most likely causative organism and appropriate initial management?
The most likely organisms are Staphylococcus aureus and Streptococcus species, and initial management is IV empiric antibiotics such as vancomycin plus ceftriaxone or cefepime, after obtaining blood and bone cultures.
A 12-year-old presents with fever, tender anterior cervical lymphadenopathy, tonsillar exudates, and no cough. Rapid strep test is positive. What is the first-line treatment and duration of therapy?
The first-line treatment is penicillin or amoxicillin orally for 10 days, because Group A Streptococcus is the most common bacterial cause of pharyngitis and beta-lactams are the drug of choice to reduce symptoms and prevent complications.
Two patients present with foul-smelling, greasy diarrhea, bloating, and weight loss after drinking untreated stream water. Patient A is a 25-year-old hiker with no significant medical history. Patient B is a 30-year-old pregnant woman with the same symptoms. How does treatment differ between these two patients and why?
Both patients have Giardia lamblia, but Patient A should be treated with metronidazole or tinidazole, while Patient B should be treated with paromomycin, because metronidazole is avoided in pregnancy and paromomycin is safer for pregnant patients.
A patient presents with an intensely pruritic, serpiginous rash on the foot after walking barefoot on a beach. The rash appears to be migrating under the skin. What is the diagnosis and treatment?
This is cutaneous larva migrans caused by hookworm, and treatment is ivermectin, because it is better tolerated and requires a shorter course than alternative therapies.
Two patients present with a homogeneous, thin, gray-white, malodorous vaginal discharge that is adherent to the vaginal walls. Patient A is not pregnant and has had three similar episodes in the past year despite treatment. Patient B is pregnant and presenting for the first time. What is the treatment for both women.
Both patients have bacterial vaginosis caused by Gardnerella vaginalis.
Patient B should be treated with oral metronidazole or clindamycin.
Patient A should be treated with oral metronidazole or clindamycin followed by a refractory/prophylactic regimen, including intravaginal boric acid, because recurrent BV requires maintenance therapy to prevent relapse.
A sexually active patient with multiple partners and inconsistent condom use asks about ways to prevent HIV infection. Who qualifies for PrEP and what medications can you prescribe?
PrEP is indicated for high-risk individuals, including those with HIV-positive partners, multiple sexual partners, or injection drug use, and consists of daily antiretroviral therapy to prevent HIV acquisition.
descovy, or truvada
A patient presents with fever, cough, and fatigue after exploring caves and cleaning bird droppings. Chest imaging shows patchy infiltrates. What is the most likely diagnosis and treatment for mild, moderate, and severe disease?
This is histoplasmosis, and treatment is itraconazole for mild to moderate disease or amphotericin B for severe disease.
A patient with a fluctuant, purulent skin abscess is suspected to have MRSA. Besides antibiotics, what is the single most important initial management step?
Incision and drainage.
A 34-year-old woman presents 24 hours after a cat bite to the hand with increasing pain, swelling, erythema, and purulent drainage. What is the most appropriate first-line treatment?
This is an infected cat bite wound, and first-line treatment is amoxicillin-clavulanate to provide broad coverage for gram-negative organisms, skin flora, and anaerobes.
A 60-year-old patient presents with rapidly progressive erythema of the thigh, severe pain out of proportion to exam, fever, hypotension, and early skin necrosis after a minor abrasion. You suspect a life-threatening soft tissue infection and start empiric IV antibiotics before surgery. Which antibiotic should be started first and why?
IV vancomycin should be started first because Staphylococcus aureus and Streptococcus species are common causes of necrotizing fasciitis, and vancomycin provides immediate broad gram-positive coverage including MRSA.
A 30-year-old presents with sore throat, fever, tonsillar exudates, and tender anterior cervical nodes, but also has a cough. Based on Centor criteria, what is the correct next step?
A rapid antigen test should be performed, because the patient scores in the 2–3 point range, which requires testing before deciding on antibiotic treatment.
An HIV patient with a very low CD4 count presents with headache, confusion, and multiple ring-enhancing brain lesions on MRI. You diagnose toxoplasmosis and start appropriate acute therapy. After clinical improvement, what long-term management is required and why?
This is toxoplasmosis, treated acutely with pyrimethamine + sulfadiazine + leucovorin, and the patient must then be placed on chronic suppression with trimethoprim-sulfamethoxazole (Bactrim) to prevent recurrence, because immunocompromised patients are at high risk for reactivation of latent infection.
A child presents with intense perianal itching, especially at night. Tape test reveals worm eggs. What is the diagnosis and first-line treatment?
This is Enterobius vermicularis (pinworm infection), and first-line treatment is mebendazole or albendazole. However mebendazole is better suited for worms in the gut.
A woman presents with thick, white, clumpy vaginal discharge described as “cottage cheese,” with intense pruritus and erythema. She has a history of recent broad-spectrum antibiotic use and poorly controlled diabetes. What is the diagnosis and treatment?
This is Candida vulvovaginitis, and treatment is fluconazole Candida overgrowth is promoted by broad-spectrum antibiotics, pregnancy, diabetes, immunocompromise, and tight/silk underwear, all of which disrupt normal vaginal flora.
A healthcare worker experiences a needle-stick injury from a known HIV-positive patient. Within what time frame must post-exposure prophylaxis be started to be effective?
PEP must be started within 72 hours of exposure, because delayed initiation significantly reduces its effectiveness in preventing HIV infection.
An HIV patient with CD4 count of 60 presents with headache, fever, neck stiffness, and altered mental status. CSF shows encapsulated yeast. What is the diagnosis and treatment?
This is cryptococcal meningitis, and treatment is amphotericin B plus flucytosine followed by fluconazole.
A healthcare worker presents with cellulitis and purulent drainage after a needle stick. Which oral agents from your materials would appropriately cover MRSA in an outpatient setting?
Trimethoprim-sulfamethoxazole, doxycycline, or clindamycin.
This disease can be a febrile illness with subacute regional lymphadenopathy. Most people with a high fever and regional lymphadenopathy have a spontaneous resolution within 2-4weeks. Very rarely does the disease become severe and disseminated.
Cat scratch disease
A patient with known sickle cell disease presents with fever and localized vertebral bone pain. Imaging confirms hematogenous osteomyelitis. Based on the most likely organism in this population, what pathogen should you suspect and what empiric antibiotic regimen is recommended after cultures are obtained?
The most likely organism is Salmonella, and empiric therapy should be vancomycin plus a 3rd or 4th generation cephalosporin after blood and bone cultures.
A child was treated appropriately for streptococcal pharyngitis but presents two weeks later with dark urine and periorbital edema. Why did antibiotic therapy fail to prevent this complication?
This represents acute glomerulonephritis, which is not prevented by antibiotic treatment, because it is an immune-mediated complication rather than direct bacterial damage.
A 22-year-old college student presents with cyclic fevers, chills, sweats, and headache after returning from travel to a region where malaria is endemic. He is hemodynamically stable, alert, tolerating oral intake, and has no signs of organ dysfunction. Blood smear confirms malaria. What is the most appropriate initial treatment?
This is uncomplicated malaria, and treatment is chloroquine, because stable patients with non-severe disease can be treated with oral antimalarial therapy.
A patient presents with chronic RUQ abdominal pain, diarrhea, fatigue, hepatosplenomegaly, jaundice, hemoptysis, and hematuria after freshwater exposure in an endemic area. You suspect a parasitic fluke infection. What is the most likely organism class and treatment?
This is a trematode (fluke) infection, and treatment is praziquantel, because trematodes cause systemic and GI disease and are treated with broad-spectrum anti-fluke therapy.
A woman returns from what she describes as a “sexual awakening journey” and presents with acute dysuria, mucopurulent cervical discharge, and unilateral conjunctivitis. She weighs 180 kg. Her best friend, who is pregnant, presents with the same symptoms after returning from the journey as well. What is the most appropriate treatment regimen for each patient and why?
Both patients should be treated for Neisseria gonorrhoeae with ceftriaxone, but the 180 kg patient requires a higher dose (1 g IM) due to weight-based dosing, while the pregnant patient receives the standard dose.
The non-pregnant patient should also receive doxycycline for concomitant Chlamydia coverage, whereas the pregnant patient must receive azithromycin instead, because doxycycline is contraindicated in pregnancy.
An HIV patient with no systemic symptoms is found to have a CD4 count of 45. You want to prevent Mycobacterium avium complex (MAC) infection. What prophylaxis is indicated and when is it safe to stop?
The patient should begin azithromycin or clarithromycin prophylaxis, because MAC prophylaxis is indicated when CD4 < 50, and it can be discontinued once CD4 > 100 for at least 3 months.
An HIV patient with CD4 count of 120 presents with progressive dyspnea, dry cough, hypoxia, and diffuse interstitial infiltrates on chest imaging. What is the diagnosis and treatment, and when should steroids be added?
This is Pneumocystis jirovecii pneumonia, and treatment is trimethoprim-sulfamethoxazole (Bactrim), with prednisone added if the patient is hypoxic, because steroids reduce inflammation and improve outcomes in moderate to severe PCP.
A patient with chronic lymphedema develops a sharply demarcated, bright red, painful facial rash with fever. Which organism is most likely responsible and why does this matter for drug selection?
Group A Streptococcus, which requires beta-lactam coverage.
A 20 year old female presents with a human bite to the back of her neck that she received 6 hours prior. The patient stated she went to the park where she got caught up in a zombies vs aliens game. She got labeled and alien and was bit by a "zombie". The bite mark is erythematous, there seems to be minimal swelling, and non-purulent. What antibiotics should she be given?
First line treatment for a human bite that is not infected is amoxicillin/clavulanate.
A patient presents with acute monoarticular knee pain, swelling, fever, and inability to bear weight. Gram stain is negative and there is no STI risk. What is the most likely organism and empiric treatment?
The most likely organism is Staphylococcus aureus, and empiric treatment is IV vancomycin, because staph is the most common cause of non–STI-related septic arthritis.
A 45-year-old presents with facial swelling, gingival pain, and fever after several days of untreated dental caries. Exam shows signs of a polymicrobial oral infection. The patient has a documented penicillin allergy. What is the most appropriate empiric antibiotic choice and why?
The most appropriate empiric treatment is azithromycin or clindamycin, because odontogenic infections are polymicrobial and normally treated with amoxicillin or penicillin, but penicillin-allergic patients require a macrolide or clindamycin for adequate coverage.
A 27-year-old patient presents with blurred vision, floaters, and eye pain. Fundoscopic exam shows focal areas of retinal inflammation and scarring. The patient reports frequent exposure to cat feces. What is the most likely diagnosis and appropriate treatment?
Toxoplasmosis caused by Toxoplasma gondii, and treatment is pyrimethamine plus sulfadiazine with leucovorin, because toxoplasma commonly causes ocular disease with retinal involvement and requires combination therapy to prevent permanent vision loss.
A patient with a history of exposure to undercooked pork presents with new-onset seizures, headaches, and signs of increased intracranial pressure. Brain imaging shows multiple cystic lesions. What is the diagnosis and treatment?
This is cysticercosis caused by Taenia solium, a pork tapeworm, and treatment is albendazole or praziquantel, because larval cysts in the brain cause neurocysticercosis leading to seizures and increased ICP.
A pregnant patient presents with a painless genital ulcer and later develops neurologic symptoms consistent with neurosyphilis. She reports a severe penicillin allergy.
1. What is the correct management?
2. Hos would treatment differ if she were not pregnant and had no neurosyphilis symptoms?
This is syphilis caused by Treponema pallidum, and in pregnancy she must undergo penicillin desensitization and receive IV penicillin, because penicillin is the only effective treatment to prevent congenital syphilis.
A non-pregnant patient with penicillin allergy could be treated with doxycycline or ceftriaxone.
An HIV patient has no respiratory symptoms but a CD4 count of 180. You are concerned about the risk of Pneumocystis jirovecii pneumonia (PCP). What prophylaxis should be initiated and when can it be discontinued?
The patient should start primary prophylaxis with trimethoprim-sulfamethoxazole (SMX-TMP) because PCP prophylaxis is indicated when CD4 < 200, and it can be stopped once CD4 > 200 for at least 3 months.
A patient from the Midwest presents with chronic cough, weight loss, and verrucous skin lesions along with pulmonary symptoms. What organism is most likely responsible and what is the treatment for mild, moderate, and severe disease?
This is blastomycosis, and treatment is itraconazole for mild disease or amphotericin B for severe disease.
A 7-year-old presents with numerous spreading, painless, honey-colored crusted lesions on the face and arms, with mild fever. You suspect impetigo. Which empiric oral antibiotic should be prescribed and why?
Oral cephalexin, because severe impetigo should be treated with systemic antibiotics that cover Staphylococcus aureus and Streptococcus species.
A 65 year old female presents 20 hours after a puppy mauled her hand for a blueberry muffin. She has increasing pain, swelling, erythema, but no purulent drainage. Grandma is allergic to penicillin, last time she took it she had an anaphylactic reaction. What is the most appropriate first-line treatment?
Clindamycin plus SMX/TMP.
So to break this down. The 1st line is Augmentin, but gammy is allergic. So we need strep/staph, gram negative, and anaerobic coverage. Clindamycin is good for anaerobes, gram positives (strep and staph), but unreliable for gram negatives. Now you have an option between Bactrim or fluoroquinolones. Bactrim adds gram negatives + MRSA, and fluoroquinolones adds gram negative. Both have their own ADR, however, fluoroquinolones have the black box warning for tendonitis in elderly people. Because gammy is old she is more at risk to develop MRSA and we dont need to give her tendonitis, so the correct option here is Bactrim.
A sexually active 22-year-old presents with acute swollen, painful knee and purulent synovial fluid. What organism must be assumed and what is first-line treatment?
Neisseria gonorrhoeae must be assumed, and first-line treatment is IV or IM ceftriaxone,- and doxycycline 100mg PO, because gonorrhea is the most common cause of septic arthritis in young sexually active patients.
Add in doxycycline to cover for chlamydia because gonorrhea and chlamydia co-infect at times.
A patient with a recent dental infection develops bilateral submandibular swelling with posterior tongue displacement and difficulty swallowing. What antibiotic strategy should be initiated and why?
The patient should be started on broad-spectrum antibiotics such as amoxicillin/clavulanate or clindamycin (works if penicillin allergic), because Ludwig’s angina is a severe complication of odontogenic infection requiring aggressive polymicrobial coverage.
A 45-year-old patient presents with fever, altered mental status, hypotension, and laboratory evidence of organ dysfunction after recent international travel. Blood smear confirms malaria. What is the most appropriate treatment and why?
This is severe malaria, and treatment is IV artesunate, because critically ill patients with organ involvement require rapid-acting intravenous antimalarial therapy.
A child is diagnosed with pinworms and treated appropriately, but symptoms return two weeks later, he gets treated again and another two weeks later the cycle continues. What additional management step should have been taken?
All household contacts should be treated simultaneously, because pinworms are highly contagious and reinfection is common if the entire family is not treated.
A patient presents with a small, painless genital ulcer followed by painful unilateral inguinal lymphadenopathy (buboes). What is the most likely diagnosis and treatment?
This is lymphogranuloma venereum caused by Chlamydia trachomatis, and treatment is doxycycline.
If the patient is pregnant she would get azithromycin.
An asymptomatic HIV patient has a CD4 count of 90. You are concerned about his decision to adopt 4 stray cats. What prophylaxis should be started and when can it be discontinued?
The patient should start SMX-TMP prophylaxis because toxoplasmosis prophylaxis is indicated when CD4 < 100, and it can be stopped once CD4 > 200 for at least 3 months.
A patient develops fever, cough, fatigue, and arthralgias after traveling to the Southwestern United States and coming in contact with a desert fungus. Imaging shows pulmonary infiltrates. What is the diagnosis and treatment?
This is coccidioidomycosis (Valley fever), and treatment is fluconazole.