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Select the ONE answer that is BEST in each case.
A 24-year-old woman complains of pain in the upper chest every time she eats or drinks anything. She is HIV positive, but currently not on any antiretroviral therapy. Her last CD4 count was 400/mL.
All forms of T-lymphocyte deficiency/ dysfunction are characterized by candidal infections. Candida species can cause thrush, skin lesions, esophagitis, and cystitis. Hematogenous spread can occur and disseminate the organism widely in individuals with low CD4 counts.
A 67-year-old man has back pain and newly discovered hypercalcemia. Further investigations determine that he has multiple lytic lesions, anemia, and a monoclonal protein in his serum. A bone marrow aspirate confirms the diagnosis of multiple myeloma.
Patients with myeloma have defects in humoral immunity and are prone to recurrent pneumonias due to S. pneumoniae. Lung infections with S. aureus and Klebsiella pneumoniae are also frequent. E. coli and other Gramnegatives cause recurrent urinary tract infections.
A 34-year-old woman is at a family picnic where she has a ham sandwich and potato salad. Three hours after the meal, she feels nauseous and throws up.
The preformed toxin of Staphylococcus causes nausea within 1–6 hours of ingestion. Ham, poultry, potato and egg salad, mayonnaise, and cream pastries are common food sources.
A 22-year-old university student is backpacking in South America. Ten days after arriving, she develops symptoms of anorexia, malaise, and abdominal cramps followed by a sudden onset of watery diarrhea. There are no symptoms of fever or chills, and the stools are nonbloody.
Enterotoxigenic E. coli causes 15–50% of traveler’s diarrhea, depending on geographic location. The incubation period is more than 16 hours, and water and many foods can be the source.
A 24-year-old man is traveling in Southeast Asia. He is eating at local restaurants and from street vendors. He now develops high fevers, anorexia, and frequent passage of small-volume stools containing blood, pus, and mucus. This is associated with severe abdominal cramps and painful straining when having bowel movements
Shigella causes an invasive diarrhea with blood and has an incubation period of more than 16 hours. Potato and egg salad, lettuce, and raw vegetables are common food sources.
A 27-year-old woman is on holiday on the East coast of the United States. She is at a seafood restaurant and has fresh shellfish for dinner. Twenty-four hours later, she develops symptoms of nausea, vomiting, abdominal cramps, and watery diarrhea.
Vibrio cholerae causes profuse watery diarrhea with an incubation period of more than 16 hours. Shellfish are a common source.
A family of four has dinner at a local Asian restaurant, where multiple dishes are ordered and shared amongst the group. Three hours after the meal, all members develop stomach symptoms consisting of nausea and vomiting.
B. cereus causes an early onset of food poisoning when found in fried rice. This occurs within 1–6 hours and, like staphylococcal food poisoning, is characterized by vomiting. The enteric form of B. cereus food poisoning is characterized by watery diarrhea and occurs 8–16 hours after ingestion of contaminated food such as meat, vegetables, dried beans, or cereals.
A 19-year-old man is seen in the office 9 days after a hiking trip in Colorado. Five days ago, he developed a fever, headache, myalgia, and nausea. Two days later, he noticed the start of a nonitchy rash on his wrists and ankles. He presents today because of light-headedness while standing and progression of the rash on to his body. He reports that he had numerous insect bites during his hike. On examination, his blood pressure is 90/60 mm Hg, pulse 100/min, and respirations 20/min. There are multiple 1–5 mm macules on his body and some of them have a hemorrhagic center consistent with petechia. His heart sounds are normal, lungs clear, and legs are edematous. Which of the following is the most likely diagnosis?
The location of infection, the possibility of tick exposure, and the nonspecific nature of the presentation are consistent with a rickettsial infection, likely RMSF.
A 22-year-old sexually active man presents with painful urination. He reports no joint symptoms, rash, fever, or penile discharge. Examination of the prostate, testes, and penis are normal, and there is no visible discharge that can be expressed from the urethra. Which of the following is the most appropriate initial diagnostic test?
The diagnosis is usually made by proximal to distal “milking of the urethra” and showing evidence of a purulent or mucopurulent discharge. Other methods include examining a urethral swab or the sediment from the first 20–30 mL of voided urine (after the patient has not voided for several hours). Dysuria without inflammation may represent a functional problem and usually does not benefit from antibiotics.
A 25-year-old woman has new symptoms of fever, headache, myalgia, and macular rash. She recently went on a camping trip with friends to the South-Central United States. She endured many “bug bites” during the trip but does not specifically recall any tick bites. The rash consists of macules 3 mm in size on her hands and feet. A clinical diagnosis of RMSF is made and she is started on treatment. Serology is drawn to confirm the diagnosis. Which of the following is the most appropriate treatment choice for this condition?
Doxycycline is the treatment of choice, with tetracycline as the second choice. There is insufficient evidence to determine the exact role of fluoroquinolones in RMSF. Beta-lactam antibiotics, erythromycin, and aminoglycosides are of no value. Sulfa-containing drugs may actually exacerbate the condition. Glucocorticoids have not been shown to be helpful, but meticulous control of volume status is important
A 21-year-old man presents with cough, headache, malaise, and fever. He reports minimal whitish sputum production and now has chest soreness from coughing so much. He has no other past medical history and no risk factors for HIV. On examination, his temperature is 38.3C, pharynx is normal, and lungs are clear. CXR reveals diffuse bilateral infiltrates. Mycoplasma pneumonia is considered in the possible differential diagnosis of his pneumonia. Which of the following skin manifestations is most likely seen in mycoplasma pneumonia?
Although all the skin problems listed have been described with M. pneumoniae infection, the only clearly linked entity is erythema multiforme.
A 23-year-old university student presents with painful urination and penile discharge. He is sexually active, and reports no joint symptoms, rash, or fever. Examination of the prostate, testes, and penis are normal, and there is a visible discharge that can be expressed from the urethra. Which of the following is the most likely causative organism?
C. trachomatis causes 30–40% of cases in the United States. The exact prevalence depends on the effectiveness of Chlamydial control programs in the population. The other organisms can all cause urethritis in men.
A 22-year-old woman complains of vulvar itching, burning, and pain when voiding urine. She has no other symptoms of fever, vaginal discharge, or urinary frequency. Physical examination reveals some vulvar ulceration but no vaginal discharge. The ulcers are small 2–3-mm lesions with an erythematous base. Which of the following is the most likely diagnosis?
HSV and C. albicans are the common causes of vulvar infection. Although they can cause dysuria, it is of the “external” variety (i.e., secondary to urine passing over the inflamed vulvar area). The other infections cause “internal dysuria” and/or vaginal discharge.
A 34-year-old woman presents with symptoms of fever, headache, and myalgia. She recently returned from a camping trip to the SouthCentral United States. She endured many insect bites during the trip but does not specifically recall any tick bites. On examination her neck is supple, heart sounds are normal, and lungs are clear. She does have a rash consisting of macules 3 mm in size on her hands, feet, and upper body. A clinical diagnosis of RMSF is made and treatment is started. Serology is drawn to confirm the diagnosis. Which of the following sites is the major target for intracellular injury by this infectious agent?
Pulmonary and systemic microcirculation are the primary targets of the disease. The resultant damage results in increased vascular permeability. This can cause edema, decreased plasma volume, decreased albumin, prerenal azotemia, and even hypotension. Involvement of the pulmonary microcirculation can result in noncardiogenic pulmonary edema
A 29-year-old sexually active man presents with painful urination and penile discharge. He reports no joint symptoms, rash, or fever. Examination of the prostate, testes, and penis are normal, and there is a visible discharge that can be expressed from the urethra. Microscopic examination of the appropriate specimens is not possible in this clinic. Which of the following is the most appropriate next step in management?
Empiric treatment should include coverage for both Chlamydial infection (with azithromycin) and N. gonorrhoeae infection (usually with ceftriaxone). There are numerous alternatives for N. gonorrhoeae infection, such as oral cefixime (not available in the United States), oral ciprofloxacin, or intramuscular (IM) ceftriaxone. However, resistance to penicillin is too common to allow the routine use of this drug.
A 56-year-old previously healthy man is admitted to the hospital for community-acquired pneumonia. He is started on empiric antibiotics. Two days later, his blood cultures are positive of S. pneumoniae. Which of the following statements concerning the epidemiology of S. pneumoniae is correct?
There is a definite midwinter spike in bacteremia in adults, but not in children. Invasive disease is highest in children under 2 years of age. Bacteremia is more common in certain groups (e.g., Native Americans, Native Alaskans, African Americans), suggesting a genetic predisposition. Up to 40% of healthy children and 10% of healthy adults are asymptomatic carriers. In adults, the organism can persist in the nasopharynx for up to 6 months.
A 62-year-old woman presents with fever, cough, sputum production, and pleuritic chest pain. CXR reveals a right middle lobe infiltrate, and she is started on antibiotics for the treatment of pneumonia. Her sputum Gram stain is positive for S. pneumoniae. Which of the following immunologic mechanisms is the most specific host defense against pneumococcal infection?
The most specific immunologic defense is directed at capsular antigens and is serotype specific. Antibodies are not naturally occurring, but are the result of prior colonization, infection, or vaccination. Intact spleen, complement and macrophage function is important in clearance of pneumococci from sterile areas, but specific immunoglobulin G (IgG) antibody coating of a pneumococcal polysaccharide capsule is essential for macrophages to ingest and kill the bacteria.
A 5-year-old boy presents with ear pain and fever. The left eardrum is inflamed with a small perforation in it and pus is seen in the external canal. A swab of the area grows S. pneumoniae. Which of the following is the most likely mechanism for S. pneumoniae to cause otitis media?
Infections of the middle ear, trachea, sinuses, bronchi, and lungs are caused by direct spread from nasopharyngeal colonization. Disease of the CNS, heart valves, bones, joints, and peritoneal are usually caused by hematogenous dissemination.
A 31-year-old woman presents with symptoms of vulvar itching and burning made worse by urinating. She has no fever or frequency, but has noticed a recent whitish vaginal discharge. Clinical examination reveals vulvar erythema, edema, and fissures. On speculum examination, there is a white discharge with small white plaques loosely adherent to the vaginal wall. Which of the following treatments is appropriate for her asymptomatic male sexual partner?
There is no need to investigate or treat an asymptomatic male partner. If candidal dermatitis of the penis is present, topical azole therapy would be appropriate.
A 29-year-old man is seen in the office after returning from a hiking trip in Colorado. He complains of feeling unwell and reports symptoms of fever, myalgia, headache, and nausea. Two days ago, he noticed a rash on his wrists and ankles that has now spread to his body. He recalls having had numerous insect bites during his trip. On examination, his blood pressure is 90/60 mm Hg, pulse 100/min, and respirations 20/min. There are multiple 1–5 mm macules on his body and some of them have a hemorrhagic center consistent with a petechia. His neck is supple and fundi are normal. The heart sounds are normal, lungs clear, and legs are edematous. Cranial nerve, motor and sensory examination is normal. A clinical diagnosis of RMSF is made and he is started on appropriate therapy. Which of the following is the most common type of central nervous system (CNS) presentation in this condition?
Although all these can be manifestations of RMSF, encephalitis as manifested by confusion or lethargy is by far the most common CNS manifestation. It occurs in about one-quarter of cases, and can progress to coma.
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