A 17-year-old girl has had fatigue and malaise for the past 10 days. Early in the course she had a mild pharyngitis. On physical examination, she has enlarged and tender posterior cervical, axillary, and inguinal lymph nodes. Her liver edge is slightly tender and the spleen tip is palpable. She has mild scleral icterus. A CBC shows Hgb 13.3 g/dL, Hct 40%, MCV 93 fL, platelet count 263,000/microliter, and WBC count 9300/microliter with WBC differential count of 45 segs, 3 bands, 25 lymphs, 15 atypical lymphs, 10 monos, and 2 eos. Which of the following infectious agents is most likely responsible for these findings?

A Hepatitis A virus

B Rubeola

C Epstein-Barr virus

D Rubella

E Human immunodeficiency virus infection

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A 25-year-old man with a history of intravenous drug use has had one bout of Pneumocystis carinii (jirovecii) pneumonia which was successfully treated. However, he now has progressive visual loss for the past month. On physical examination he has decreased visual acuity bilaterally, but no papilledema. Laboratory studies show Hgb 13.8 g/dL, Hct 41.2%, MCV 92 fL, platelet count 182,000/microliter, and WBC count of 3700/microliter with WBC differential count of 74 segs, 4 bands, 10 lymphs, 10 monos, and 2 eos. Which of the following organisms is most likely causing his visual problems?

A Candida albicans

B Staphylococcus aureus septicemia

C Pneumocystis carinii (jirovecii)

D Cytomegalovirus

E Mycobacterium avium-intracellulare

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A 29-year-old G2 P1 woman has had a worsening vaginitis for the past week, marked by a profuse, clear, watery vaginal discharge and itching, since she became pregnant 3 months ago. She has developed urinary frequency along with dysuria in the past 2 days. Her husband also develops dysuria. A cytologic smear of the vaginal fluid reveals few neutrophils and lymphocytes, but there are small rounded organisms with flagella. Which of the following infectious agents is most likely responsible for these findings?

A Candida albicans

B Neisseria gonorrheae

C Gardnerella vaginalis

D Trichomonas vaginalis

E Chlamydia trachomatis

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A 5-year-old girl develops a mild watery diarrhea that lasts for about 3 days and is accompanied by a low-grade fever and vomiting. On physical examination she has a temperature of 37.4 C. Laboratory studies include a stool for ova and parasites which is negative. She recovers without therapy and has no sequelae. Which of the following infectious agents most likely caused her illness?

A Shigella flexneri

B Adenovirus

C Vibrio parahemolyticus

D Rotavirus

E Salmonella

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A 31-year-old G3 P2 woman is in the second trimester. Her prior pregnancies ended with delivery of normal term infants who are still living. She has an ultrasound performed because of lack of fetal movement by 18 weeks, and the scan shows that the fetus is hydropic. TORCH titers are performed on maternal blood, and there is an increased Toxoplasma gondii IgM titer. Which of the following pathologic findings is most likely to be present in this fetus?

A Cervical lymph node enlargement

B Keratitis

C Cerebral inflammation with calcification

D Pneumonia alba

E Congenital cardiac defects

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A 92-year-old woman has dysuria for a week, followed by fever and chills. On physical examination her temperature is 38.9 C. She has right costovertebral angle tenderness. Laboratory studies include a blood culture positive for E. coli. Her blood pressure decreases to 80/40 mm Hg. Which of the following mechanisms has most likely caused her blood pressure to decrease?

A Myocardial failure

B Vasodilation

C Hemorrhage

D Thrombosis with embolism

E Renal failure

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If a man with a risk factor of intravenous drug use became infected with human immunodeficiency virus (HIV) in the year 2000, then which of the following findings is most likely to occur?

A His first complication indicative of AIDS will be development of Kaposi's sarcoma

B He will develop clinical AIDS by the year 2010

C He cannot spread HIV infection to others until he develops clinical AIDS

D Use of an antiretroviral drug such as zidovudine will prevent AIDS from occurring

E His CD4 lymphocyte count will not drop below 200/microliter

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A 38-year-old man has had a chronic cough and fever for over a month. On physical examination his temperature is 37.8 C. A chest radiograph reveals a miliary pattern of small 2 to 4 mm nodules scattered throughout all lung fields. Infection with which of the following organisms has most likely occurred in this man?

A Staphylococcus aureus

B Mycobacterium tuberculosis

C Influenza A virus

D Pneumocystis carinii (jirovecii)

E Chlamydia trachomatis

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Several children in the neighborhood develop perianal itching, most pronounced at night. Their parents don't pay much attention to this until they develop the same problem. Laboratory studies are performed on all affected persons with the "scotch tape slide test." The eggs recovered from the perianal region of affected persons are 50 microns, flat, and embryonated. Which of the following parasitic infections are these persons most likely to have?

A Enterobius vermicularis

B Ascaris lumbricoides

C Trichuris trichiuria

D Necator americanus

E Strongyloides stercoralis

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A 19-year-old previously healthy woman develops a severe, voluminous, watery diarrhea over the course of two days. The volume of diarrhea is so severe that she becomes hypotensive, and on admission to the hospital she has a serum sodium of 165 mmol/L. Gross examination of the diarrhea fluid reveals flecks of mucus; on microscopic examination there are few white blood cells and no red blood cells. A blood culture is negative. She receives intravenous fluids and recovers within a week. Which of the following infectious agents is most likely to be present in her diarrhea fluid?

A Rotavirus

B Shigella flexneri

C Vibrio cholerae

D Salmonella typhi

E Giardia lamblia

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A veterinarian working in Claremont, California, in the foothills of the San Gabriel mountains, saw his physician because of marked axillary and inguinal lymph node swelling developing over the course of only a day. On physical examination vital signs show T 38.6 C, P 100/minute, RR 20/minute, and blood pressure 85/55 mm Hg. He has right axillary tender lymphadenopathy. A lymph node biopsy is performed and on microscopic examination shows marked necrosis with hemorrhage, and a Gram stain shows numerous gram-negative bacilli. He is most likely to be infected with which of the following organisms?

A Francisella tularensis

B Leptospira interrogans

C Borrelia burgdorferi

D Yersinia pestis

E Bacillus anthracis

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Which of the following sites in the body should not be found routinely to be colonized by bacterial growth?

A Floor of mouth

B Skin of hands

C Cecum

D External ear

E Alveoli

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A 17-year-old girl has an eruption of small 2 to 8 mm vesicles on the skin of her upper lip that have appeared over the past week. On physical examination she is afebrile. The vesicles are clear and, when ruptured, become very painful to touch. A cytologic smear of fluid from a vesicle reveals a cluster of multinucleated cells with mauve intranuclear inclusions. This eruption subsides over the next two weeks. These findings are most characteristic for infection with which of the following viruses?

A Herpes simplex virus

B Parvovirus

C Cytomegalovirus

D Adenovirus

E Epstein-Barr virus

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Over the course of a week, 5 neonates in the Newborn Intensive Care unit develop sepsis with methicillin-resistant Staphylococcus aureus (MRSA). This outbreak is most likely related to which of the following?

A Extensive cephalosporin antibiotic use

B A failure of infection control measures

C Neural tube defects in the neonates

D Visitation of the neonates by the parents

E Contaminated formula from the vendor

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A newborn male born at 35 weeks gestation is noted to have marked hydrops fetalis. The baby exhibits poor motor and sensory function. An MRI scan shows evidence for extensive periventricular leukomalacia. Microscopy performed on a urine sample shows a large cell with a large nuclear inclusion surrounded by a halo. These findings are most characteristic for congenital infection with which of the following viruses?

A Echovirus

B Coxsackievirus

C Cytomegalovirus

D Herpes simplex virus

E Human immunodeficiency virus

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In an experiment, the activation of chemical mediators at the site of infection is analyzed using different infectious organisms. It is observed that complement activation via the alternate pathway occurs more often with some infections than others. Which of the following organisms is most likely to produce alternate pathway complement activation?

A Staphylococcus aureus

B Treponema pallidum

C Klebsiella pneumoniae

D Mycobacterium tuberculosis

E Candida albicans

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Three days after a weekend swimming party at a neighbor's house, all the children in a family develop eye irritation. On physical examination they have red eyes with conjunctival hyperemia. The children are better in a week without therapy, with no major sequelae. Which of the following infectious agents is most likely to cause the illness in these children?

A Adenovirus

B Chlamydia trachomatis

C Rotavirus

D Staphylococcus aureus

E Candida albicans

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A 31-year-old previously healthy woman has developed a low volume diarrhea over the past 2 days. On physical examination her temperature is 37.4 C. A stool sample is dark and is positive for occult blood. Colonoscopy is performed and reveals a friable mucosa with superficial ulcerations extending from the rectum to the cecum. Three days later she has a serum urea nitrogen of 25 mg/dL and creatinine of 2.2 mg/dL. Her condition improves with antibiotic therapy. Which of the following infectious agents is most likely to produce these findings?

A Staphylococcus aureus

B Shigella flexneri

C Cryptosporidium parvum

D Campylobacter jejuni

E Vibrio cholerae

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A retrospective clinical study is performed to assess the risk for serious infection with standard medical and surgical procedures. The medical records of patients are reviewed to quantify the infectious complications that occurred following performance of procedures in hospital. It is observed that despite use of proper technique, there is still some risk for infection. Which of the following procedures is most likely to be found as the safest for patients, with the fewest nosocomial infections?

A General anesthesia for tooth extraction

B Foley catheter placement for two weeks

C Nasogastric tube insertion

D Laparotomy

E Intravenous catheter placement for a week

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A 38-year-old G3 P2 woman gives birth at 35 weeks gestation to an infant male noted to have marked generalized hydrops fetalis. The mother did not note any significant problems during the pregnancy, except for a mild facial skin rash in the second trimester. The infant has no congenital anomalies noted on physical examination. Laboratory studies show that the infant's hemoglobin is 7.6 g/dL with hematocrit 23.1%. Which of the following congenital infections is most likely to be present in this infant?

A Herpes simplex virus

B Rubella

C Parvovirus

D Rotavirus

E Cytomegalovirus

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While labelling a tube of blood drawn from a patient, you drop the tube on a table top and it breaks. Which of the following disinfectants is most appropriate to use in this situation?

A 3% Hydrogen peroxide

B 0.5% Sodium hypochlorite

C 10% Neutral buffered formalin

D 1% Quaternary ammonium chloride

E 50% Ethanol

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A 48-year-old man has had a worsening painful sore in his mouth for the past 2 weeks. On physical examination there is a lesion starting at the gingiva and extending to the right floor of the mouth which exhibits induration with draining sinus tracts to the overlying skin. A radiograph reveals mandibular osteomyelitis. There is some granular, yellowish-orange material in the exudate. Which of the following microscopic findings is most likely to be present in a smear of the exudate?

A Short, broad, non-septate hyphae

B Thin, branching, septate hyphae

C Long gram positive filaments

D Short acid fast bacilli

E Long acid fast filaments

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A 7-year-old girl has been ill with fever, irritability, and a bloody diarrhea for the past 3 days. Two days later the child exhibits marked malaise and is taken to the physician. On physical examination she has a temperature of 37.9 C. She has periorbital edema. Laboratory test findings include a serum creatinine of 4.3 mg/dL with urea nitrogen of 38 mg/dL. A renal biopsy is performed and microscopic examination shows multiple fibrin thrombi in the glomerular capillary loops. She is placed on hemodialysis and recovers in 3 weeks. A verotoxin elaborated by which of the following organisms is the most likely cause for her renal disease?

A Escherichia coli

B Staphylococcus aureus

C Salmonella typhi

D Campylobacter jejuni

E Entameba histolytica

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A 26-year-old man notes the appearance of a dark red-black encrusted area on his right arm. This is at the site of removal of a tick 3 days before. He then develops a widespread hemorrhagic skin rash over the next 4 days. On physical examination this rash involves trunk and extremities, and even his palms and soles. Then, small 0.2 to 0.4 cm foci of skin necrosis develop on his fingers and toes. He then develops a non-productive cough. Which of the following infectious agents is most likely to produce these findings?

A Francisella tularensis

B Borrelia burgdorferi

C Bacillus anthracis

D Bartonella henselae

E Rickettsia rickettsii

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A 22-year-old man is involved in a motor vehicle accident in which the vehicle goes off the road and into a muddy drain ditch. On physical examination he has multiple lacerations and contusions on both his legs. Five days later he develops marked swelling of his left leg. The overlying skin has large bullous vesicles that rupture and are foul-smelling. Palpation reveals that the underlying soft tissues are crepitant. A fasciotomy is performed, and there is extensive myonecrosis. Which of the following organisms is most likely to be cultured from the muscle of his left leg?

A Streptococcus pyogenes

B Clostridium perfringens

C Staphylococcus aureus

D Bacteroides fragilis

E Actinomyces israeli israeli

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A 25-year-old man has noted the appearance of reddish skin lesions increasing in size and number for over the past month. On physical examination, there are 0.5 to 1.5 cm maculopapular erythematous, non-ulcerated, lesions of his face, wrists, elbows, and knees. There is decreased sensation to light touch in these lesions. There is also loss of sensation in his hands and feet. He has normal motor strength and deep tendon reflexes. A biopsy of one of the skin lesions is performed and on microscopic examination there are extensive dermal infiltrates of macrophages that on acid fast stain are filled with numerous short bacilli. Which of the following drugs is most likely to be efficacious in treating this man?

A Isoniazid

B Ciprofloxacin

C Prednisone

D Cytoxan

E Dapsone

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A 17-year-old boy has had a fever for the past 2 days. On physical examination he has a temperature of 37.4 C. He has lymphadenopathy and oral thrush. Laboratory studies show an HIV-1 RNA of 5500 copies/mL, a CD4 lymphocyte count of 175/microliter, and a positive HIV test by ELISA and confirmed by Western blot. Which of the following stages of HIV infection is he most likely to have?

A Early acute HIV infection

B Recent seroconversion

C Risk for opportunistic infection

D Congenital HIV infection

E Latency of infection

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A 61-year-old man with diabetes mellitus has developed pain and swelling over the right side of his face over the past two days. Laboratory findings include serum sodium 139 mmol/L, potassium 4.8 mmol/L, chloride 108 mmol/L, CO2 9 mmol/L, and glucose 281 mg/dL. Urinalysis reveals 4+ glucose, 4+ ketones, 1+ protein, and no blood. A CT scan of the head shows bony erosion around the paranasal sinus. A Gram stain of an aspirate from this site reveals broad, non-septate hyphae. These findings are most indicative of infection with which of the following organisms?

A Coccidioides immitis

B Treponema pallidum

C Cryptococcus neoformans

D Mucor circinelloides

E Actinomyces israeli israeli

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A clinical study is performed with subjects admitted to the hospital with infectious diseases. It is observed that some infections are complicated by elaboration of exotoxins and some by elaboration of endotoxins by the infectious organisms. These toxins are found to produce different patterns of organ damage. Which of the following complications is most likely to be produced by an endotoxin?

A Myocarditis

B Tetanic muscular contractions

C Severe watery diarrhea

D Septic shock

E Muscular paralysis

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A 12-year-old boy has been active all summer long, but then becomes febrile over the past 3 days. Two weeks later, he begins to exhibit loss of motor function in his right lower extremity. Three months later, he is left with residual weakness of his right leg. Which of the following microscopic pathologic abnormalities involving the nervous system is most likely to be present in this boy?

A Lymphocytic infiltrates around dorsal root ganglia

B Negri bodies in Purkinje cells of the cerebellum and in hippocampal neurons

C Eosinophilia of neurons in the motor cortex

D Mononuclear inflammatory cell infiltrates with loss of anterior horn cells

E Wallerian degeneration of the femoral and tibial nerves

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A 37-year-old man with progressive dementia and loss of motor function over the past two years is found to be HIV positive. A CT scan of the brain shows mild cerebral atrophy. His neurologic decline is most likely to be caused by which of the following complications of his HIV infection?

A Cryptococcal meningitis

B Large B cell lymphoma

C HIV encephalitis

D Toxoplasma gondii abscesses

E Mycobacterium avium-complex granulomas

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A 60-year-old woman has had fevers for the past 2 months. On physical examination her temperature is 37.7 C. She has axillary lymphadenopathy. A chest radiograph shows enlarged hilar lymph nodes. A lymph node biopsy is performed and on microscopic examination shows non-caseating granulomata with fibrosis, but a Ziehl-Neelsen stain shows no acid-fast bacili. Which of the following is the most likely diagnosis?

A Silicosis

B Scleroderma

C Mycobacterium avium-complex infection

D Byssinosis

E Sarcoidosis

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A 6-year-old previously healthy boy has had a fever along with swelling and tenderness of his face for the past 3 days. On physical examination, the swelling is seen bilaterally in the region of the parotid glands. He also has tenderness of the testes in the scrotum. He is improved in a week, with no sequelae. Which of the following viruses is the most likely cause for this boy's illness?

A Coxsackie virus

B Echovirus

C Mumps virus

D Epstein-Barr virus

E Adenovirus

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A 41-year-old man has had a chronic cough with fever for the past 3 months. On physical examination his temperature is 37.6 C. He has decreased breath sounds over the right upper lung. A chest radiograph shows a cavitary 4 cm nodule in the right upper lobe along with adjacent smaller nodules with calcifications. Which of the following is the most likely diagnosis?

A Small cell anaplastic (oat cell) carcinoma with lipid pneumonia

B Bronchopneumonia with Pseudomonas aeruginosa

C AIDS with cytomegalovirus

D Secondary tuberculosis

E Peripheral organizing septic pulmonary thromboembolus

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A 9-year-old girl has developed high fevers over the past 3 days. The highest temperature spikes to 40 C occur several hours apart. She becomes obtunded. On physical examination she appears pale. No skin rashes are present. Laboratory findings include Hgb 8.2 g/dL, Hct 25.1%, MCV 103 fL, platelet count 176,000/microliter, and WBC count 11,900/microliter. Serum electrolytes reveal sodium 131 mmol/L, potassium 6.2 mmol/L, chloride 89 mmol/L, CO2 19 mmol/L, glucose 71 mg/dL, creatinine 2.1 mg/dL, and urea nitrogen 25 mg/dL. A head CT scan reveals marked cerebral edema. A chest radiograph reveals bilateral pulmonary edema. Which of the following findings is most likely to be seen on her peripheral blood smear?

A Small blue ring forms in erythrocytes

B Corkscrew shaped spirochetes

C Microfilariae

D Gram negative diplococci in neutrophils

E Plasma cells

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A 29-year-old woman has had malaise for 2 weeks. She now has a cough productive of frothy sputum. On physical examination she is afebrile. She has pedal edema. A chest radiograph reveals pleural effusions, pulmonary edema, and a globally enlarged heart. Auscultation of the chest reveals an irregular heart rate but no murmurs. A routine sputum gram stain and culture shows no pathogens. Which of the following is the most likely causative virus for her cardiac disease?

A Poliovirus

B Cytomegalovirus

C Adenovirus

D Hantavirus

E Coxsackie B virus

F Influenza A virus

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A pathologic study is conducted with autopsy cases in which a microscopic diagnosis of granuloma was made in the gastrointestinal tract. The histologic appearances, special stains, microbiologic culture reports, and clinical histories are reviewed to determine the etiologies for granuloma formation. It is observed that most gastrointestinal granulomas with caseous necrosis are the result of an infectious etiology. Which of the following diseases is most likely to produce this type of granuloma in the GI tract?

A Cryptosporidoisis

B Amebiasis

C Enterobiasis

D Salmonellosis

E Tuberculosis

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A clinical and pathologic study is conducted with cases in which a pulmonary nodule is diagnosed. It is observed that there is a subset of cases in which a nodule on chest CT scan has bright attenuation at the periphery and on pathologic examination demonstrates vascular invasion, thrombosis, and hemorrhage. Patients with this form of pulmonary nodule are found to be immunocompromised. Which of the following infectious agents is most likely to produce this pattern of disease?

A Actinomyces israeli israeli

B Aspergillus flavus

C Bacillus anthracis

D Corynebacterium diptheriae

E Pneumocystis carinii (jirovecii)

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A 70-year-old man presents with severe headache and nuchal rigidity of one day's duration. On physical examination he has a temperature of 37.9 C. He does not have papilledema. A lumbar puncture is performed and the cerebrospinal fluid obtained is cloudy. The CSF cell count shows 20,000 WBC's/microliter (>99% neutrophils). The CSF glucose is 38 mg/dl (serum glucose 98), and protein 82 mg/dl. Which of the following findings with gram staining of the CSF is most likely to be present in this patient?

A Short, thin gram negative rods

B Gram positive diplococci

C Gram negative cocci in neutrophils

D Large gram negative rods

E Large gram positive cocci in clumps

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A 41-year-old woman has noted a ring-like rash 5 cm in diameter involving the skin of her right calf, along with fever, for the past 3 days. On physical examination her temperature is 37.5 C. She has enlarged tender lymph nodes palpable in the right inguinal region. These findings subside in two weeks' time. A month later she is bothered by arthralgias and myalgias. Serologic testing is positive for Borrelia burgdorferi. Two years later she develops a debilitating arthritis involving knees and hips. Which of the following routes of infection most likely occurred in this woman?

A Aerosolized droplet nuclei

B Sexual intercourse

C Scratch from a cat

D Deer tick bite

E Drinking downstream from the herd

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Molecular studies are performed to determine the nucleic acid content of viral infecting humans. It is observed that viruses can contain RNA or DNA. Which of the following viruses is most likely to have a genome of RNA?

A Human immunodeficiency virus

B Cytomegalovirus

C Adenovirus

D Herpes simplex virus

E Hepatitis B virus

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A 24-year-old woman has been bothered by painful lesions in her genital region for the past week. On physical examination she has multiple groups of 0.2 to 0.4 cm clear vesicles on the perineum. Which of the following methods is the quickest and most inexpensive way to diagnose the etiologic agent for her genital infection?

A Serologic titer

B Viral culture

C Cytologic smear

D Darkfield examination

E Polymerase chain reaction on fluid

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Several high school students from Saratoga, Wyoming, went out hunting rabbits. They skinned, cooked, and ate the rabbits they obtained, though the meat was tough and gamey and required lots of chili sauce to make it palatable. About 3 weeks later, one student developed an ulcerative pustule on his left forefinger. Over the next week he developed axillary adenopathy with fever, chills, and myalgia. Which of the following organisms is most likely causing an infection in this student?

A Francisella tularensis

B Yersinia pestis

C Listeria monocytogenes

D Pseudomonas pseudomallei

E Brucella abortus

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In an experiment, Escherichia coli organisms are studied to determine the relationship of bacterial structure to clinical findings. It is observed that some strains of E. coli recovered from cultures of hospitalized patients have plasmids. Which of the following clinical characteristics of infection is most likely to occur when plasmids are present in these strains of E. coli?

A Antibiotic resistance

B Fever and chills

C Latency

D Exotoxin-mediated injury

E Carcinogenesis

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A laboratory study is performed to determine the optimal method for diagnosis of Treponema pallidum infections in hospitalized patients. The sensitivity, specificity, cost, and adherence to collection technique are analyzed for several diagnostic methods. The desired test should pick up as many cases as possible, with few false negatives, and have a low cost. Which of the following laboratory tests is most likely to fulfill these criteria?

A FTA-ABS

B RPR

C Sed rate

D WBC count

E VDRL on CSF

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