Infections and Inflammatory Diseases - High-Yield Conditions

Explore common staining techniques for identifying infectious organisms, including giemsa, gram, acid-fast, and specialized stains, and learn which organisms resist staining like mycoplasma, legionella, chlamydia, and rickettsia.

Dengue fever is a viral infection transmitted by Aedes mosquitoes, presenting with rash, arthralgia, and bleeding from low platelets and WBCs, self-limiting over 2–3 weeks.

Lyme disease from borrelia via deer tick has three stages: erythema migrans, carditis, and encephalopathy with arthritis. Treatments include doxycycline, amoxicillin in pregnancy, and IVIg for neurological symptoms.

Explain prion PrPsc converting PrPc into a beta sheet form, causing noninflammatory axonal vacuolation and spongiform brain disease, with Jakob disease, bovine spongiform encephalopathy, and kuru.

Identify zika virus as a flavivirus with an RNA genome, transmitted by aedes mosquitoes and sexually or placentally, causing conjunctivitis, rash, microcephaly, and requiring supportive care.

Use the 'grams target fetal cells' mnemonic to identify meds to skip during pregnancy, including griseofulvin, ribavirin, aminoglycosides, macrolides, sulfonamides, tetracyclines, fluoroquinolones, and chloramphenicol.

Screen for group b streptococcus at 37 weeks and treat positive cases with intravenous penicillin, especially with fever during delivery, preterm birth, prolonged rupture, or prior GBS.

Listeria thrives in raw meat and unpasteurized dairy, crosses the placenta, and uses intracellular transmission. Encounter septicemia, meningitis, or abortion among immunocompromised patients; healthy individuals have milder gastroenteritis.

Identify melasma, or chloasma, the mask of pregnancy, a benign acquired hyperpigmentation caused by hyperfunctioning melanocytes producing more melanin during pregnancy or with oral contraceptive pills, resolving after pregnancy.

Differentiate gram-negative intracellular gonococci and meningococci, noting IgA protease; gonococci lack a capsule and spread sexually, while meningococci have a capsule, ferment glucose (meningococci also maltose), and spread by droplets.

Chlamydia is an obligate intracellular organism with a life cycle of infectious elementary bodies and reticular bodies, diagnosed by Giemsa stain or fluorescence antibodies, and treated with azithromycin or doxycycline.

Explore the eight herpesviruses, detailing transmissions from respiratory and saliva to sexual contact, and hallmark diseases like labialis on the lips, keratoconjunctivitis, genital ulcers, shingles, mononucleosis, retinitis, and Kaposi sarcoma.

Explain HIV prophylaxis thresholds for PCP, histoplasmosis, and toxoplasmosis, with CD4-guided folic inhibitors and itraconazole in endemic areas, plus herpes zoster immunoglobulins and secondary herpes prophylaxis.

Human papillomavirus causes skin warts transmitted by skin-to-skin contact, even with condoms. Warts are highly contagious, usually non-cancerous, but vaccination prevents infection and cancer risk.

Explore torch infections overview, including toxoplasma, rubella, CMV, HIV, HSV-2, and syphilis; review vertical transmission and common neonatal signs like blueberry muffin rash, cataracts, deafness, hydrocephalus, and PDA.

Kaposi sarcoma is a malignant endothelial cell cancer caused by HIV or HHV-8, presenting as reddish, raised lesions anywhere, including the respiratory tract, with lymphocyte infiltrates on biopsy.

Food poisoning affects about one in seven people annually, causing cramps, diarrhea, nausea, vomiting, and fever; stay hydrated with electrolyte fluids, and consult a doctor before OTC remedies.

Vomiting points to Staphylococcus aureus with preformed toxins, onset about six hours and lasting 2–3 days. Bloody diarrhea suggests salmonella or shigella, with campylobacter as a second common cause.

Identify major foodborne pathogens such as Campylobacter, E. coli, Listeria, Norovirus, Salmonella, and Staphylococcus aureus, and practice proper handling, washing, and cooking to prevent food poisoning.

Campylobacter jejuni transmits via fecal-oral routes in camping settings, shows corkscrew motility with flagella, causes bloody diarrhea, and can precede reactive arthritis or Guillain-Barré syndrome; treated with fluoroquinolones or erythromycin.

Celiac disease is a gluten-triggered, t-cell mediated condition that damages intestinal villi in the duodenum, causing malabsorption. Diagnosis shows IgA anti-transglutaminase, anti-endomysial, and anti-gliadin antibodies; treatment requires a gluten-free diet.

Explore hepatitis types a through e, their transmission, incubation, progression from acute to chronic, cancer risks for b and c, pregnancy risk for e, and histology including councilman bodies.

Diverticulitis inflames sigmoid diverticula, causing left lower abdominal pain with diarrhea or constipation and fever or bleeding. Diagnose by ct or colonoscopy; treat with antibiotics and high-fiber diet; surgery rarely.

Whipple disease is an intestinal infection caused by the gram-positive intracellular bacterium Tropheryma whipplei that causes villous atrophy, foamy macrophages in the lamina propria, and a positive PAS stain.

An exotoxin inhibits acetylcholine receptors, causing descending flaccid paralysis in botulism, diagnosed by toxin detection; adults acquire it from undercooked food, infants from honey-associated spores.

Explore Clostridium difficile pathogenesis with toxin A and toxin B, diagnostic PCR, pseudomembranous colitis, antibiotic use especially clindamycin, and treatments including metronidazole, vancomycin, fidaxomicin, and fecal microbial transplant.

Clostridium tetani releases tetanospasmin, blocking GABA and glycine signaling in Renshaw cells, causing spastic paralysis with sardonicus and trismus; treat with antitoxins and vaccinate at two months for high-risk newborns.

Explore virulence factors of Staphylococcus aureus and others, including protein A, protein M, IgA protease, type three secretion system, serpentine cord factor, sulfatides, and the K capsule.

Antibiotic resistance spreads when a bacterium isolates a resistance gene by transposition, becomes F+, and transfers the gene and sex palace to an F− partner via a mating bridge.

Explore how bacteriophages infect bacteria and mediate gene transfer, with lytic phages causing generalized transduction and lysogenic phages causing specialized transduction that can confer exotoxin production, heat, and antibiotic resistance.

Explain transformation, or competence, where bacteria uptake naked DNA from the environment and gain antibiotic resistance, unless a DNA lysing agent degrades the DNA.

Explain transposition, where small parts of bacterial DNA are excised to form plasmids, then reintegrated into chromosomes, enabling transfer of functions among bacteria.

Describe antigenic shift via reassortment in co-infected cells, producing progeny, explain bar mnemonic for four virus groups, and distinguish drift, phenotypic mixing, recombination, and complementation with hepatitis B and D.

Abscesses are a pus collection, usually caused by Staphylococcus aureus, most often in the skin. Drain large abscesses first, then consider antibiotics; culture recurrent or risky cases to guide therapy.

Explain how the pilosebaceous unit, plug formation, and sebum accumulation with Propionibacterium acnes-driven inflammation lead to comedones, pimples, and pustules, and mention isotretinoin as effective yet highly teratogenic.

Anthrax, caused by gram-positive Bacillus anthracis, forms spores and toxins, with Medusa's head colony and a glutamate layer resisting antibiotics; cutaneous eschar forms, pulmonary form with 100% mortality.

Identify atopic dermatitis as a type I hypersensitivity eczema with immediate histamine release and elevated IgE, presenting as a pruritic eruption with facial involvement in infancy and links to asthma.

Bacillary angiomatosis, caused by Bartonella, causes vascular, pedunculated skin and organ lesions in immunocompromised patients. Diagnosis by biopsy and treatment with antibiotics; prognosis worsens with brain or bone involvement.

Learn about bartonella bacillary angiomatosis, a disease seen in homeless and immunocompromised patients after cat scratches, presenting as pedunculated angiomas, diagnosed by biopsy and treated with doxycycline.

Bullous pemphigoid, a type two hypersensitivity with autoantibodies to hemidesmosomes, causes tense blisters that heal without scarring and spare mucosal membranes; immunofluorescence at epidermal-dermal junction accompanies a negative Nikolsky sign.

Identify cellulitis as a progressive skin infection beneath the surface, often caused by Staphylococcus aureus or Streptococcus pyogenes. Check for collections and drain pus when present, then treat with antibiotics.

The varicella zoster virus causes chickenpox and can reactivate as shingles, typically affecting a single dermatome with vesicles and red papules. Treatment involves a cycle of air.

Identify erysipelas as a well demarcated red area affecting the dermis and superficial lymphatics, caused by Streptococcus pyogenes. Diagnose erysipelas clinically and treat with antibiotics to prevent bacteremia.

Identify erythema multiforme as redness with multiple shapes, including target lesions, vesicles, bulla, and macules. Learn its infectious and drug triggers, then remove the trigger and re-examine for resolution.

Identify impetigo as a superficial epidermal infection with honey-colored crusts, highly contagious, caused by Staphylococcus aureus or Streptococcus pyogenes; antibiotics render patients non-contagious after one day, enabling school return.

Molluscum contagiosum is a poxvirus infection presenting as umbilicated papules, often transmitted sexually in adults, spreading to the armpits and behind the knees. It is self-limiting; isolation is the management.

Necrotizing fasciitis is a deep skin infection that starts below, with pain out of proportion and early healthy-appearing skin, often with gas and purple bullae; aggressive debridement and antibiotics follow.

Identify pityriasis rosea signs, including herald patch and a christmas tree distribution trunk rash, and learn its self-resolving course over about two months with itch relief.

Identify tuberculosis by PPD skin test, IGRA, or biopsy, with chest x-ray and sputum analysis providing initial clues, and emphasize isolation and treatment for confirmed TB.

Identify pseudofolliculitis barbae as an inflammatory shaving-related condition, in dark-skinned males, producing painful, pruritic, hyperpigmented papules on cheeks, jawline, and neck; treat with alternative shaving or antibiotics in severe cases.

Identify pyogenic granuloma as a polypoid, red capillary hemangioma that mimics a granuloma, often bleeds and links to pregnancy or trauma, treat with silver, nitrates, or excision/laser.

Examine epidermal skin infections such as impetigo, folliculitis, and erysipelas, then describe deeper dermal infections and the progression to cellulitis, necrotizing fasciitis, and myonecrosis.

Staphylococcus produces a toxin that disrupts keratinocyte attachment in the stratum granulosum, causing skin separation and Nikolsky sign; it affects newborns and those with renal insufficiency, requiring admission and antibiotics.

Compare the spectrum of severe cutaneous adverse reactions: staph-related disease in newborns, Stevens-Johnson syndrome with mucosal involvement, and toxic epidermal necrolysis from medications.

Identify tinea corporis, or ringworm, as a fungal infection spread by skin-to-skin contact, with a slowly expanding circular, itchy rash; diagnose with Koh and treat with topical azoles or terbinafine.