Question 1

A 33-year-old man is being treated in the hospital for new-onset seizures. He has no notable medical history. Vital indicators are typical. A neurological examination reveals no anomalies. A 3-cm cystic lesion in the temporal lobe is seen by a CT scan of the head. The mass is removed, and the histopathology is depicted in the figure below:  Which of the following is the most likely diagnosis?

Accepted Answer

Eductional Objective: Neurocysticercosis is a helminth infection caused by the consumption of Taenia solium eggs. In people from an endemic location, it frequently manifests as adult-onset seizures. 1 cystic brain lesion is seen by imaging. The presence of a scolex, the anterior section of the worm with hooks and suckers, is indicative of the existence of the parasite.

Question 2

A 26-year-old man is brought to the emergency department because of abdominal pain, nausea, and vomiting for the past 1 hour. The patient has not had diarrhea or fever. Two hours ago, he ate a sandwich ,potato salad and coleslaw during summer cookout in a park,. He has no history of serious illness and takes no medications. He appears ill. His temperature is 37.6°C (99.6°F), pulse is 80/min, and blood pressure is 122/68 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 98%. Cardiac examination shows no abnormalities. The lungs are clear to auscultation. Abdominal examination shows diffuse mild tenderness with no rigidity, rebound, or guarding. His symptoms quickly resolve with supportive care.  Which of the following strategies would have been most effective in preventing this patient's illness?

Accepted Answer

Eductional Objective: Staphylococcal foodborne illness is due to the consumption of a preformed enterotoxin in contaminated food.  Most cases can be prevented by washing hands thoroughly prior to food preparation (prevents contamination) and ensuring proper refrigerated storage (prevents bacterial proliferation/enterotoxin production).

Question 3

A 17-year-old boy comes to the emergency department because of a 3-day history of pain in his left wrist. That morning the pain increased and he started to have chills and malaise. Last week he had self-resolving left knee pain. He is otherwise healthy and has not had any trauma to the wrist. He recently returned from a camping trip to Minnesota. He is sexually active with one female partner, who uses a diaphragm for contraception. His temperature is 38.7°C (101.7°F). Examination shows several painless violaceous vesiculopustular lesions on the dorsum of both wrists and hands; two lesions are present on the left palm. There is swelling and erythema of the left wrist with severe tenderness to palpation and passive movement. Gram-negative bacteria isolated from this patient's blood produce an enzyme that splits the IgA molecule at the hinge region.  Which of the following is likely to be the most important role of this bacterial enzyme in the course of the infection?

Accepted Answer

Eductional Objective: IgA protease is produced by Neisseria meningitidis, N gonorrhoeae, Streptococcus pneumoniae, and Haemophilus influenzae.  This enzyme cleaves secretory IgA at its hinge region, rendering it ineffective.  Secretory IgA exists on mucosal surfaces and in secretions and acts to bind and inhibit the action of pili as well as other cell surface antigens that normally mediate mucosal adherence and subsequent penetration.

Question 4

A 22-year-old woman comes to the physician because of urinary frequency, pelvic discomfort, and purulent urethral discharge following unprotected sex with a new partner. She has a history of chronic ear infections and asthma. Her only medication is a combined fluticasone-albuterol inhaler. She does not smoke cigarettes and drinks alcohol socially up to 4 times per week. Her temperature is 36.0°C (96.8°F), pulse is 70/min, and blood pressure is 125/80 mm Hg. Nucleic acid amplification testing is positive for Neisseria gonorrhoeae infection.  The patient develops antibody against the bacterial pili that enhance attachment to host cells.  Her symptoms resolve with adequate treatment. Several weeks later, the patient develops N gonorrhoeae reinfection after repeat exposure to the same partner.  Which of the following is the most likely reason for the lack of long-lasting immunity against the bacteria despite antibody formation in this patient?

Accepted Answer

Eductional Objective: Gonococci use their pili to mediate adherence to the mucosal epithelium.  Through antigenic variation, each gonococcus can modify the pilus protein expressed, thereby avoiding host defenses (to some degree) and making vaccination directed against the pilus protein difficult.

Question 5

A 5-year-old boy is brought to the emergency department by his grandmother because of difficulty breathing. Over the past 2 hours, the grandmother has noticed his voice getting progressively hoarse and occasionally muffled, with persistent drooling. He has not had a cough. His grandmother is unsure if patient's immunizations are up-to-date. He appears uncomfortable and is sitting up and leaning forward with his chin hyperextended. His temperature is 39.5°C (103.1°F), pulse is 110/min, and blood pressure is 90/70 mm Hg. Cardiac examination reveals tachycardia and a normal rhythm without rubs or murmurs.  The abdomen is soft and nondistended.  Which of the following additional signs is most likely to be found on examination?

Accepted Answer

Eductional Objective: Laryngeal airway obstruction can occur with epiglottitis.  It leads to inspiratory stridor due to the dynamic collapse of the larynx during inspiration.

Question 6

A 17-year-old boy comes to the emergency department because of a 3-day history of pain in his left wrist. That morning the pain increased and he started to have chills and malaise. Last week he had self-resolving left knee pain. He is otherwise healthy and has not had any trauma to the wrist. He recently returned from a camping trip to Minnesota. He is sexually active with one female partner, who uses a diaphragm for contraception. His temperature is 38.7°C (101.7°F). Examination shows several painless violaceous vesiculopustular lesions on the dorsum of both wrists and hands; two lesions are present on the left palm. There is swelling and erythema of the left wrist with severe tenderness to palpation and passive movement. Which of the following strategies would most likely have prevented this patient's current condition?

Accepted Answer

Eductional Objective: Neisseria gonorrhoeae is spread sexually by genitourinary secretions and can be prevented by the consistent use of condoms.  Genitourinary infections are often asymptomatic, which increases the risk of spread through the bloodstream, leading to disseminated gonococcal infection.  Patients with disseminated disease typically present with the triad of polyarthralgia, tenosynovitis, and dermatitis or purulent arthritis.

Question 7

A 4-year-old boy is brought to the emergency department for evaluation of a fever for 1 day. The mother reports that he has had severe pain in his lower extremities and difficulty eating since yesterday. He has not had a cough, nausea, or vomiting. He was born at term and has been healthy. His immunizations are up-to-date. He appears irritable. His temperature is 38.5°C (101.3°F). Examination shows several flesh-colored, tender papules over the trunk, knees, palms, and soles. There are multiple 2-mm, reddish macules on the hard palate. The remainder of the examination shows no abnormalities. The infectious agent most likely responsible for this patient's current condition is also associated with which of the following?

Accepted Answer

Eductional Objective: Hand-foot-and-mouth disease (oral ulceration and extremity rash) and herpangina (oral ulcerations without rash) are the most common manifestations of enteroviral infection.  Rare but serious complications of infection include myocarditis and central nervous system disease (eg, aseptic meningitis).

Question 8

A 3-month-old male is brought to the emergency department because of fever and poor feeding for 2 days. He became very fussy the previous evening and cried for most of the night. The mother does not recall any sick contacts at home. He appears irritable. His temperature is 38.6°C (101.5°F), pulse is 180/min, and blood pressure is 82/51 mm Hg. Examination shows scleral icterus. He becomes more agitated when picked up. There is full range of motion of his neck and extremities. The anterior fontanelle feels soft and flat. A lumbar puncture is performed, and the results of cerebrospinal fluid (CSF) analysis are as follows:  Gram-negative coccobacilli are isolated from the CSF.  These organisms demonstrate little growth on 5% sheep blood agar but grow well when incubated on the same media alongside colonies of Staphylococcus aureus.  Staphylococci promote the growth of these bacteria by supplementing which of the following substances?

Accepted Answer

Eductional Objective: Haemophilus influenzae is a "blood-loving" organism that requires X (hematin) and V (NAD+) factors for growth.  This can be accomplished by growing H influenzae in the presence of Staphylococcus aureus and demonstrating the "satellite phenomenon," whereby H influenzae grow only near the B-hemolytic S aureus colonies that produce the needed X and V factors.

Question 9

A 1-day-old male newborn is brought to the emergency department because of fever and poor feeding for 2 hours. He became very fussy the previous evening and cried for most of the night. He was born at 36 weeks' gestation and weighed 2430 g (5 lb 3 oz) to a 21-year-old woman who came to the emergency department in active labor with ruptured membranes; she had not received adequate prenatal careHe appears irritable. His temperature is 38.6°C (101.5°F), pulse is 180/min, and blood pressure is 82/51 mm Hg. Examination shows scleral icterus. He becomes more agitated when picked up.Blood samples are obtained, and empiric antibiotics are initiated for the treatment of sepsis.  Cultures on blood agar grow bacterial colonies with a narrow zone of clear hemolysis.  When these bacteria are grown in the presence of Staphylococcus aureus, the zone of hemolysis is enhanced around the staphylococcal colonies.  Which of the following is the most likely pathogen infecting this patient?

Accepted Answer

Eductional Objective: Streptococcus agalactiae (group B Streptococcus), one of the most common causes of early neonatal sepsis, is typically identified by the presence of a narrow zone of beta-hemolysis when plated on blood agar.  It is also identified by the production of CAMP factor, which enhances beta-hemolysis by particular strains of Staphylococcus aureus.

Question 10

A 29-year-old man who recently immigrated to the United States comes to the physician for a routine health maintenance examination. He has no history of serious illness. His mother has hypertension and his father died of testicular cancer at the age of 51 years. He does not smoke or drink. He is sexually active and uses condoms consistently. He takes no medications. His immunization records are unavailable. He works as a financial consultant and will go on a business trip to Mexico City in 6 weeks. His temperature is 36.7°C (98.7°F), pulse is 78/min, and blood pressure is 122/78 mm Hg. Cardiopulmonary examination shows no abnormalities. Laboratory studies show:  The patient's country of origin does not offer universal immunization against hepatitis A, and he says he has not been vaccinated against the virus.  Which of the following do these laboratory findings most likely suggest?

Accepted Answer

Eductional Objective: Hepatitis A virus infection is most commonly silent or subclinical ("anicteric") in young children but can also present as an acute, self-limited illness characterized by jaundice, malaise, fatigue, anorexia, nausea, vomiting, right upper-quadrant pain, or an aversion to smoking.

Question 11

A 41-year-old man comes to the physician because ofintermittent rectal bleeding and itching for 2 weeks. He has a history of HIV infection for which he takes zidovudine, emtricitabine, and efavirenz. he has been sexually active with 3 male partners. He uses condoms inconsistently. Digital rectal examination and anoscopy show an exophytic mass on the anal margin that is protruding into the anal canal. The mass is tender to palpation and bleeds easily on contact. Laboratory studies show a leukocyte count of 7,600/mm3 and a CD4+ T-lymphocyte count of 410/mm3. Which of the following factors is most likely responsible for the development of this patient's anal lesion?

Accepted Answer

Eductional Objective: Anal squamous cell carcinoma is strongly associated with human papillomavirus and typically presents with rectal bleeding, pruritus, and/or pain; examination demonstrates an ulcerated or nodular, exophytic anal lesion.  Histology reveals large, eosinophilic, hyperchromatic squamous cells arranged in islands with nuclear atypia and prominent keratinization.

Question 12

A 28-year-old woman, gravida 1, para 0, at 32 weeks' gestation comes to the physician for a prenatal visit. She has had no prenatal care. She emigrated from China 5 years ago and cannot recall all of her vaccinations. She appears well. Physical examination shows a uterus consistent in size with a 32-week gestation. Serum studies show:
Anti-hepatitis A IgM antibody negative
Anti-hepatitis A IgG antibody positive
Hepatitis B surface antigen negative
Anti-hepatitis B surface antibody positive
Hepatitis B core antigen negative
Anti-hepatitis B core antibody negative
Which of the following is the most appropriate initial action by the physician?

Accepted Answer

Eductional Objective: Infants born to HBeAg-positive mothers have a high risk of acquiring perinatal hepatitis B virus (HBV) infection.  Infected neonates have high levels of HBV replication and are at high risk for chronic infection, but are usually asymptomatic or have only mildly elevated liver function tests.

Question 13

A 59-year-old nurse woman comes to the physician following an accidental needlestick in the operating room.. She feels well. She has systemic lupus erythematosus and hypertension. She does not drink alcohol. Her current medications include lisinopril and hydroxychloroquine. She appears malnourished. Her vital signs are within normal limits. Examination shows a soft, nontender abdomen. There is no ascites or hepatosplenomegaly. Serum studies show  Which of the following statements is most likely to be true regarding the nurse's viral status?

Accepted Answer

Eductional Objective: Individuals who are successfully immunized against hepatitis B virus develop protective anti-HBs antibody.  Individuals who recover from hepatitis B infection, however, have anti-HBs as well as anti-HBc antibodies.  The presence of circulating HBsAg indicates active infection.

Question 14

A 24-year-old pregnant woman is found to have chronic viral hepatitis B on liver biopsy.  The presence of which of the following serologic markers is most likely to increase the risk of vertical transmission of the virus?

Accepted Answer

Eductional Objective: Vertical transmission of hepatitis B from pregnant females to the unborn child can occur in women with active hepatitis B infection.  The presence of HBeAg (a marker of viral replication and increased infectivity) in the mother greatly increases the risk of vertical transmission of the virus.  Because of this concern, the newborns of all mothers with active hepatitis B are passively immunized at birth with hepatitis B immune globulin (HBIG), followed by active immunization with recombinant HBV vaccine.

Question 15

A 29-year-old male is hospitalized with low-grade fever and high serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST).  His serum is positive for HBsAg.  You should inform the patient that the most likely outcome for his infection would be:

Accepted Answer

Eductional Objective: The most common outcome in HBV-infected adults (> 95%) is acute hepatitis with mild or subclinical symptoms that eventually completely resolve.

Question 16

A 32-year-old woman comes to the emergency department for a 2-week history of right upper quadrant abdominal pain. She has also been feeling tired and nauseous for the past 5 weeks. She has a history of depression and suicidal ideation. She is a social worker for an international charity foundation. She used intravenous illicit drugs in the past but quit 4 months ago. Her only medication is sertraline. Her temperature is 37.8°C (100.0°F), pulse is 100/min, and blood pressure is 128/76 mm Hg. She is alert and oriented. Scleral icterus is present. Abdominal examination shows tenderness to palpation in the right upper quadrant. The liver edge is palpated 3 cm below the right costal margin. There is no rebound tenderness or guarding. The abdomen is nondistended and the fluid wave test is negative. She is able to extend her arms with wrists in full extension and hold them steady without flapping. Laboratory studies show:  Which of the following is an essential step in the replication cycle of the virus infecting this patient?

Accepted Answer

Eductional Objective: Hepatitis B virus has a partially double-stranded DNA genome and contains a viral DNA polymerase with reverse transcriptase activity.  Reverse transcriptase serves a crucial step in viral replication; it converts transcribed positive sense single-stranded RNA into the partially double-stranded DNA genome of viral progeny.

Question 17

A 32-year-old woman comes to the physician because of a 2-month history of fatigue and muscle pain. Over the past month, she has had intermittent episodes of nausea. She has a history of intravenous drug use, but she has not used illicit drugs for the past five years. She has smoked one pack of cigarettes daily for 14 years and drinks one alcoholic beverage daily. She takes no medications. Her last visit to a physician was 4 years ago. Her temperature is 37.0°C (98.6°F), pulse is 90/min, respirations are 20/min, and blood pressure is 110/70 mm Hg. Physical examination shows jaundice and hepatosplenomegaly. There are blisters and erosions on the dorsum of both hands. The remainder of the examination shows no abnormalities. Laboratory studies show:are positive for hepatitis C virus RNA.  Six months previously, she tested negative for hepatitis C.  Without treatment, which of the following is the most likely outcome in this patient?

Accepted Answer

Eductional Objective: The most common outcome of hepatitis C infection without antiviral treatment is lifelong persistent infection (ie, chronic hepatitis C).  Of those with chronic hepatitis C, approximately 20% develop cirrhosis, and only a minority experiences complications (eg, ascites, variceal bleeding, hepatocellular carcinoma).

Question 18

An outbreak of hepatitis in New Delhi was characterized by high incidence of fulminant hepatitis in pregnant women, who experienced a mortality rate of 20%.  The virus responsible for the outbreak:

Accepted Answer

Eductional Objective: Hepatitis E virus is an unenveloped, single-stranded RNA virus spread through the fecal-oral route.  The most concerning feature of hepatitis E infection is the high mortality rate observed in infected pregnant women.

Question 19

Researchers develop a novel drug to treat HIV infection.  In an in vitro experiment, wild-type viral isolates are cultured with human CD4 T lymphocytes in the presence of the drug.  Microscopic evaluation of these cells reveals no cytopathic changes, and no intracellular viral particles can be detected.  Further analysis reveals that in the presence of the drug the virus attaches to the cellular membrane, but fusion of the viral and cell membranes does not occur.  Which of the following is the most likely target of this medication?

Accepted Answer

Eductional Objective: The chemokine receptor CCR5 is a coreceptor that enables the HIV virus to enter cells.  Blockade of CCR5 by chemokine receptor antagonists prevents viral entry into host cells.

Question 20

An infant is evaluated at the office after developing prominent oral thrush, interstitial pneumonia, and severe lymphopenia during the first year of life.  The patient was born full-term to a 25-year-old woman who received no prenatal care and has substance use disorder with intravenous drug use.  She breastfed her son for the first month but then switched to formula feedings.  The mother is currently unwilling to undergo any kind of testing.  She tells the health care provider, "Just take care of my son."  Which of the following prenatal interventions would have most likely prevented this infant's condition?

Accepted Answer

Eductional Objective: Antiretroviral therapy during pregnancy reduces the risk of perinatal transmission of HIV to 1%-2% and is recommended for all pregnant women with HIV.

Quiz 9: Microbiology and Virology

A 24-year-old pregnant woman is found to have chronic viral hepatitis B on liver biopsy. The presence of which of the following serologic markers is most likely to increase the risk of vertical transmission of the virus?

A 29-year-old male is hospitalized with low-grade fever and high serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) . His serum is positive for HBsAg. You should inform the patient that the most likely outcome for his infection would be:

An outbreak of hepatitis in New Delhi was characterized by high incidence of fulminant hepatitis in pregnant women, who experienced a mortality rate of 20%. The virus responsible for the outbreak: