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Caused by gram positive, spore-forming, anaerobic rod Clostridium tetani

Produces tetanospasmin exotoxin, a protease which cleaves SNARE proteins on GABA-ergic and glycinergic (inhibitory) synaptic vesicles in the spinal cord; excessive stimulation of muscles causes spastic paralysis and trismus (lockjaw)


Toxic Shock Syndrome

S. aureus produces TSST-1 superantigen which cross-links MHC II and TCR outside of the antigen binding site, causing massive release of IFN-y and IL-2

Presents as fever, rash, and shock



Caused by Treponema Pallidum spirochete; blood screening by VDRL/RPR test with confirmatory testing by FTA-ABS

Primary - localized disease presenting as painless chancre

Secondary - disseminated disease presenting as maculopapular rash on palms/soles + constitutional sx (fever, non-tender lymphadenopathy)

Tertiary - end-organ failure characterized by chronic granulomatous disease, syphilitic heart disease (aortic atrophy/dilation, aortic valve incompetency), neurosyphilis (dementia, Tabes Dorsalis)

Treatment: Penicillin G


Respiratory Syncytial Virus (RSV)

RSV is a common cause of bronchiolitis in premature infants

Presents like a bad cold - low grade fever, rhinorrhea, cough, respiratory distress (apnea, tachypnea, wheezing, crackles)


Lyme Disease

Caused by infection with spirochete Borrelia burgdorferi, carried by ticks in the Northeastern US

Stage 1 is characterized by flu-like illness and erythema migrans rash (bullseye); may present with facial palsy

Stage 2 (early disseminated disease) targets skin, CNS (encephalopathy, facial nerve palsy, polyneuropathy), heart (AV node block), joints

Treatment: Ceftriaxone, doxycycline


Atypical pneumonia

Clasically caused by mycobacterium pneumoniae

Causes interstitial, "walking pneumonia" - presents as headache, non-productive cough

Diagnosed by presence of cold agglutinins (IgM)

Findings: X-ray looks worse than patient with diffuse, patchy inflammation localized to interstitial areas with distribution involving > 1 lobe

Treatment: Macrolide, doxycycline, or fluoroquinolone


Bacterial endocarditis

Most often of the mitral valve, but tricuspid valve endocarditis is associated with IV drug abuse; common pathogens: staphylococcus aureus (acute), viridans streptococci (subacute)

Presents with fever, new systolic murmur secondary to tricuspid regurgitation

Complications: May seed septic emboli from the right side of the heart, resulting in pulmonary manifestations (cough, pleuritic chest pain, diffuse pulmonary infiltrates), chordae rupture, pericarditis



Most commonly caused by H. influenzae

Presents with high fever, dysphagia, drooling, inspiratory stridor, and respiratory distress

Findings: X-ray shows thickening of epiglottis (thumbprint sign)


Pneumocystis pneumonia

Opportunistic infection caused by pneumocystis jirovecii; causes pneumonia in immunocompromised hosts - HIV or post-transplant

Presents as an acute pneumonia with fever, cough, tachypnea, and hypoxia

Findings: Diffuse interstitial pneumonia on X-ray with "ground glass" appearance

Treated with TMP-SMX


Poststreptococcal glomerulonephritis

Nephritic syndrome that develops ~10 days after pharyngitis or skin infection with nephritogenic strain of Group A b-hemolytic streptococcus

Type III hypersensitivity reaction due to deposition of antigen-antibody complexes within the glomerular basement membrane, leading to complement activation

Presents with hematuria, proteinuria, oliguria, and hypertension

Treatment: Supportive; disease is self-limited



Infection caused by the Epstein Barr Virus (HHV-4)

Presents with flu-like symptoms, increasing fatigue, lymphadenopathy, and splenomegaly



Caused by Varicella Zoster Virus (VZV); spread by respiratory droplets and/or direct contact

Presents as a vesicular eruption appearing first on the trunk and alter on the face; "dew drop on a rose petal" lesions appear in varied stages of healing

Treatment: Usually self-limiting; may be treated with acyclovir, famciclovir, valacyclovir

Live-attenuated vaccine available



AKA Herpes Zoster Virus (HZV); caused by reactivation of varicella zoster virus (VZV) infection from dorsal root ganglion secondary to chickenpox

Presents as a unilateral vesicular eruption confined to a single dermatome

Treated with Acyclovir, Famciclovir, Valacyclovir

Complications: Post-herpetic neuralgia, facial nerve palsy, retinitis


Cat scratch fever

Caused by Bartonella henselae; transmitted by bite or scratch of bacteremic cats

Presents with a primary innoculation lesion, low grade fever, and regional lymphadenopathy


Rocky Mountain Spotted Fever

Caused by gram negative cocci Rickettsia Rickettsii found in southern Atlantic US, transmitted by tick vector

Clinical triad = headache + fever + rash (vasculitis of wrists, palms, soles)

Treated with doxycycline or chloramphenicol



Rotavirus = DNA Reovirus family

Most common cause of fatal diarrhea in children; common cause of acute diarrhea in US during winter months, especially in daycare centers

Causes acute nausea, vomiting, watery diarrhea, and low grade fever; self-resolves after several days but may lead to transient lactose intolerance due to destruction of lactase-producing enterocytes in the small intestine

Treatment: Fluid replacement

2 oral, live-attenuated vaccines available



Rhabdovirus family - ssRNA; transmitted by bats, raccoons and skunks; virus migrates into CNS via retrograde transport up nerve axons from site of infection with long latency before onset of symptoms (weeks-months)

Post-exposure treatment includes wound cleaning, rabies vaccine (killed virus), +/- rabies immune globulin

Presents with fever/malaise, agitation, photo/hydrophobia, paralysis, coma, and death

Findings: Negri bodies, enlarged salivary glands


3 most common pathogens found in uncomplicated UTI

1. E. coli (80%)
2. Staphylococci saprophyticus (10-15%, especially sexually active women)
3. Klebsiella pneumoniae



Caused by pathogen Leptospira interrogans found in water contaminated with animal urine; commonly seen in surfers in the tropics

Presents with flu-like illness, jaundice, conjunctival erythema, photophobia


Weil disease

AKA Icterohemorrhagic Leptospirosis

Severe presentation of leptospirosis with jaundice and azotemia due to liver/renal dysfunction, fever, hemorrhage, and anemia


H. pylori

Gram negative, comma-shaped rod associated with 70% of gastric ulcers and ~100% of duodenal ulcers in PUD

Associated chronic gastritis (antral) and increased risk of gastric adenocarcinoma and MALT lymphoma

Dx with urea breath test or endoscopy with biopsy

Treated with triple therapy (PPI + Bismuth + Tetracycline)


Entamoeba Histolytica

Protozoan pathogen transmitted via fecal-oral route through cysts in water

Presents with bloody diarrhea (dysentery), abdominal cramping / tenesmus, + liver abscess / RUQ pain

Findings: Serology shows protozoans with ingested RBCs; stool sample shows cysts; LFTs show elevated alk phos with ~ normal ALT, AST, and bilirubin

Treatment: Metronidazole, Iodoquinol


Enterohemorrhagic E. Coli

Serotype O157:H7 is most common; transmitted by contaminated meat/water leading to outbreaks

Non-invasive BUT produces Shiga-like toxin, which binds to rRNA in enterocytes and renal epithelial cells, inhibiting protein production and causing tissue damage

Presents with 5-10 days of bloody diarrhea, severe abdominal cramps, low grade fever; possible hemolytic uremic syndrome (thrombocytopenia + anemia + acute renal failure)

Treatment is supportive only - fluids +/- dialysis; antibiotics do not shorten course of dz and may increase risk of HUS


Schistosoma haematobium

Trematode parasite; snails are host, penetrates through skin of human to cause granuloma, fibrosis, and inflammation of liver and spleen

Chronic infection associated with squamous cell carcinoma of the bladder; presents with painless hematuria

Trx: Praziquantel



Caused by parasite Erlichia Chaffeensis; transmitted by Lone Star Tick)

Presents with fever, malaise, rash

Findings: Monocytes/neutrophils with "berry-like" cytoplasmic inclusions (morulae)


Respiratory Legionellosis (Legionnaire's Disease)

Severe pneumonia caused by gram negative Legionella; usually seen in older patients with risk factors (tobacco, alcohol, DM, chronic illness, etc.)

Transmitted by aeresolized droplets from environmental water source (air conditioners); no person-to-person transmission

Presents with severe pneumonia, fever, GI and CNS symptoms; milder, flu-like presentation = Pontiac Fever); antibodies can x-react with the enzyme responsible for VWF degradation leading to thrombotic thrombocytopenic purpura, intravascular hemolysis, elevated BUN/Creatinine

Dx: Presence of antigen in urine, growth on charcoal yeast extract agar

Trx: Macrolide or Fluoroquinolone



Caused by trichomonas vaginalis; responsible for 10% of women seeking STI treatment

Presents with vaginitis - vaginal pruritis, dysuria, foul-smelling, green discharge; finding of "strawberry cervix" seen

Diagnosed by the presence of mobile, flaggelated trophozoites on discharge wet prep

Treatment: Metronidazole for patient and prophylaxis for partner



Caused by gram negative pathogen Vibrio Cholera

Causes secretory (non-inflammatory, non-bloody) diarrhea; voluminous "rice water" stools without WBCs

Can lead to severe dehydration, electrolyte abnormalities, cardiac/renal failure

Treatment: Oral rehydration therapy


Pneumococcal pneumonia

Caused by streptococcus pneumoniae (alpha-hemolytic strep); optochin sensitive, gram positive diplococci

Most common cause of community acquired pneumonia, especially among adults 18-65 and the elderly

Presents with fever, chills, pleuritic chest pain, and cough productive of green/rusty sputum

Findings: Lobar findings on physical exam - dullness to percussion, bronchial breath sounds, egophany in a focal area, lobar consolidation on CXR

Treatment: Penicillins or cephalosporins; macrolides in allergic patients



Caused by polio virus with fecal-oral transmission

Virus initially infects and replicates within the pharynx and small intestine causing fever, malaise, nausea, vomiting, an diarrhea; hematogenous spread to the CNS causes death of LMNs in the anterior horn of the spinal cord

Presents with LMN signs: hypotonia, muscle weakness/flaccid paralysis, hyporeflexia, muscle atrophy; most serious complications are para/quadriplegia, respiratory muscle paralysis



Gram positive aerobe forming branching filaments; stains weakly acid-fast positive

Normally found in soil; causes pulmonary and brain abscesses in immunocompromised patients

Treated with sulfonamides

*Often mistaken for TB due to pulmonary manifestations and weakly acid-fast staining


Candida albicans

Dimorphic yeast - can form pseudohyphae or buds; catalase positive

Common cause of mucocutaneous and systemic fungal infections including: oral/pharyngeal thrush in immunocompromised patients, vulvovaginitis, diaper rash, endocarditis in IVDUs, chronic mucocutaneous candidiasis (due to T cell deficiency), chronic granulomatous disease (due to NADPH oxidase deficiency)

Treated with Nystatin (topical) or amphotericin (systemic)


Chlamydia conjunctivitis

Transmitted from infected mother to newborn upon passage through the birth canal

Presents in the newborn several days - several weeks after birth with swollen eyelids, conjunctival inflammation, and purulent discharge

Treated prophylactically with erythromycin eye drops


Respiratory Syncytial Virus (RSV)

Most common cause of bronchiolitis and pneumonia in children; most children have been exposed by age 2

Presents with cough, tachypnea, low grade fever, and mildly decreased O2 sat; crackles and expiratory wheezes heard on auscultation

Dx: Rapid serological test for viral antigen


Pulmonary Aspergillosis

Cause of fungal pneumonia in immunocompromised (neutropenic) patients; due to Aspergillus fumigatus

Presents with pleuritic chest pain, cough, hemoptysis, and dyspnea



Caused by Rubeola (paramyxovirus)

Initially presents as cough, coryza (acute inflammation of the upper respiratory mucosa), and conjunctivitis + characteristic red, maculo-papular rash which spreads from the head downward; + Koplik (blue/white) spots of buccal mucosa

Acute disseminated (post-infectious) encephalomyelitis
Subacute sclerosing panencephalitis

Live-attenuated vaccine available


Acute disseminated (post-infectious) encephalitis

Occurs as a rare complication of Rubeola (measles) infection

Causes multifocal inflammation and de-myelination of white matter in the brain and CNS; auto-immune mediated

Similar to MS but occurs as a single episode with fever and loss of consciousness


Subacute sclerosing panencephalitis

Occurs as a result of long-standing infection with measles (Rubeola virus)

Stage 1 - Behavior/personality changes, decreased memory

Stage 2 - Myoclonic spasms, increasing memory impairment

Stage 3 - Blindness, mutism, coma; fatal

Can be chronically managed (not cured) in Stage 1 with interferon, Ribavirin


Whooping Cough

Caused by gram negative rod bordatella pertussis

Produces pertussis toxin; toxin inhibits Gi, leading to overactivity of adenylate cyclase with increased production of cAMP; this leads to inhibition of phagocytosis and survival of the microbe

Presents as cough on expiration and "whooping" on inspiration


Meningococcal Meningitis

Caused by N. meningidites - 2nd most common causative organism in young adults

Presents with headache, malaise, pain with flexion and extension of the neck, + petechial / maculopapular rash on the extremities (with meningococcemia)

Labs: CSF shows elevated WBCs (primarily neutrophils), elevated protein, low glucose

Diagnosed by CSF culture on Thayer-Martin agar



Caused by the gram positive rod Corynebacterium diptheriae via a pro-phage encoded exotoxin which inhibits protein synthesis via ADP-ribosylation of EF-2

Presents with pseudomembranous pharyngitis, cervical lymphadenopathy, dysphagia

Toxoid vaccine preventable


Molluscum Contagiosum

Caused by the poxvirus

Presents as flesh-colored nodules

Transmitted to the trunk by swimming pools and towels (especially in kids) or to the genitals by sexual contact


Otitis Externa

AKA "Swimmer's Ear," often caused by Pseudomonas

Presents with ear pain, fever, erythema and tenderness of the external auricle and mandibular area


Progressive Multifocal Leukoencephalopathy (PML)

An opportunistic infection caused by re-activation of latent JC virus in the CNS

Seen in advanced AIDS patients with CD4 < 200; causes destruction of oligodendrocytes with demyelination of white matter

Presents with initial visual field deficits, mental status changes, and weakness; progresses to blindness, dementia, coma, and death within 6 months

CSF fluid analysis is unremarkable; MRI shows non-enhancing lesions


Bacterial Vaginosis

Caused by Gardernella vaginalis infection - gram-variable, pleomorphic rod

Presents as gray vaginal discharge with a fishy odor; associated with sexual activity but NOT sexually transmitted

Microscopy shows clue cells

Treated with metronidazole or clindamycin



Non-septate, branching fungal infection of the nasal cavity and sinuses

Seen mostly in ketoacidotic patients due to increased concentrations of glucose and ketones

Presents with headache, fever, facial pain, nasal discharge

Risk of meningitis if fungi penetrate through cribiform plate into CSF space

Treated with Amphotericin B


Hepatitis E

RNA Hepevirus; transmitted via fecal-oral route, common in Sub-Saharan Africa

Presents acutely with nausea, vomiting, and abdominal pain associated with low-grade fever

High mortality in pregnant women


Staphylococcal toxic shock syndrome

Caused by release of TSST-1 toxin by S. aureus; TSST-1 is a super-antigen that non-specifically cross-links MHCII and TCR leading to clonal T-cell proliferation with massive release of IFN-y and IL-2

Presnts with fever, hypotension, desquamating rash, and end organ damage



A paramyxovirus clasically infecting the parotid glands and testes

Presents with swollen neck and parotid glands, orchitis, and asceptic meningitis; risk of infertility, especially after puberty


Brucella Melitensis

Intracellular, gram negative coccobacilli; acid fast

Enters the body through contaminated milk or direct contact with infected live stock

Presents with undulating fever, weakness, loss of appetite



Caused by intracellular, gram negative rod Francisella Tularensis; carried by rabbits, transmitted to humans by flea or tick bite

Presents as a well-demarcated, ulcerative lesion with a black base


Actinomyces israelli

Gram positive anaerobe found in normal oral flora

Causes orofacial abscesses which drain yellow pus that demonstrates "sulfur granules"

Treated with IV penacillin x 2-4 weeks followed by oral penicillin or amoxicillin x 6-12 months


St. Louis Encephalitis

Due to an arthropod-transmitted Flavivirus; most commonly seen in the Mississippi River Valley

Most common cause of epidemic encephalitis in the US; also causes meningitis

Treatment is supportive; no specific antiviral medications exist


Chagas Disease

Caused by South American protozoa Trypanosoma cruzi; transmitted by the painless bite of the Reduviid bug ("kissing bug")

Presents as dilated cardiomyopathy, megacolon, megaesophagus

Romana sign characteristic of acute phase