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Select the ONE answer that is BEST in each case.
A 22-year-old recent immigrant to the United States has never been vaccinated for tetanus. He sustains a minor, but soil-contaminated, injury. Which of the following statements is correct?
In tetanus, an acute onset is usual. The median onset is 7 days, and 90% present within 14 days of injury. The organism is an anaerobic, motile Gram-positive rod. It has the ability to survive for years in the form of spores, which are resistant to disinfectants and heat. Tetanus can occur in nonimmunized individuals, or those who have neglected their booster shots. Penicillin, or metronidazole, is used in treatment, but their efficacy is not clear.
A 19-year-old man has donated blood for the first time. Despite having no risk factors for human immunodeficiency virus (HIV) infection, his blood tests positive for HIV by enzyme immunoassay (EIA). Which of the following statements is correct?
EIA is an excellent screening test for HIV infection as it is positive in over 99.5% of cases. However, it lacks specificity, and in low risk populations, only about 10% of EIA positive results are true positives. Recent influenza vaccination, acute viral infections, and liver disease are common causes for false positives. The Western blot test is more specific and is the usual confirmatory test, although even more specific tests are now available.
A 27-year-old man presents with symptoms of fever, chills, malaise, and joint discomfort in his hands and knees. He looks unwell, his temperature is 39.4C, blood pressure 115/70 mm Hg, pulse 110/min, head and neck is normal, and his jugular venous pressure (JVP) has a prominent c-v wave. There is also a 3/6 pansystolic murmur heard at the right sternal border that increases with respiration. His lungs are clear, abdomen is soft, and hand joints are normal. He has multiple puncture sites on his forearms from injection drug use. Which of the following is the most likely causative organism?
S. aureus causes more than 50% of cases of native valve endocarditis in drug abusers. The onset is usually acute, and the tricuspid valve is the most commonly affected. In staphylococcal tricuspid endocarditis, septic pulmonary emboli are common. Frequently, no murmur is heard.
A 23-year-old woman develops vesicular lesions on an erythematous base on her vulvar area. She has tender lymphadenopathy and dysuria as well. Which of the following is the most likely causative organism?
HSV-2 genital infections may be associated with fever, malaise, and anorexia. Vesicular lesions usually ulcerate rapidly and become covered with exudate. There is a 90% chance of recurrent symptoms in the first year following a primary infection. HSV-1 genital infections are similar, but the chance of recurrence is less
A 34-year-old man is traveling in Southeast Asia on business. He is staying in Western-style hotels and eating food in large restaurants. He has not eaten from street vendors. One week after arrival, he develops symptoms of anorexia, nausea, and abdominal cramps followed by the sudden onset of watery diarrhea. He has no fever or chills and there is no blood or pus in the stools. Which of the following is the most appropriate therapy for his condition?
Current recommendations suggest that mild diarrhea be treated with oral rehydration alone, but when enteric symptoms such as cramps are bothersome, treatment with loperamide or bismuth subsalicylate is warranted. More severe infections with severe diarrhea, severe pain, or fever should be treated with antibiotics such as fluoroquinolones or trimethoprim-sulfamethoxazole.
An 18-year-old woman presents with headache, anorexia, chilly sensations, and discomfort on both sides of her jaw. She has also noticed discomfort in both lower abdominal quadrants. Physical examination reveals bilateral enlarged parotid glands that are doughy, elastic, and slightly tender; with a reddened orifice of Stensen’s duct. Her abdomen is soft with bilateral lower quadrant abdominal tenderness; a temperature of 38.5°C; and a pulse rate of 92/min. Laboratory data show hemoglobin 13 g/dL; hematocrit 40%; white blood cells (WBC) 9000/mL, with 35% segmented neutrophils, 7% monocytes, and 58% lymphocytes. Which of the following is the most likely cause for her abdominal pain and tenderness?
Pain referring to either or both lower quadrants is common when oophoritis is present. Fever usually accompanies oophoritis. Sterility is not a consequence of mumps oophoritis.
A 32-year-old man, previously well, develops a fever and dry cough. On examination, his chest is clear and heart sounds are normal. A chest x-ray (CXR) reveals a diffuse interstitial infiltrate. Which of the following is the most likely causative organism?
Mycoplasmas have no cell walls and have filtration characteristics of viruses, but morphologically are closer to bacteria. The typical M. pneumoniae infection produces an influenzalike respiratory illness characterized by headache, malaise, fever, and cough. If pneumonia occurs, physical examination can be relatively benign despite a grossly abnormal CXR.
A 25-year-old man is admitted with fever and rust-colored sputum. He looks unwell, temperature 38.4C, pulse 100/min, and blood pressure 115/80 mm Hg. On auscultation, there are bronchial breath sounds in the right axilla and inspiratory crackles. The CXR is shown in Fig. Which of the following is the most likely diagnosis?
The x-ray shows a silhouette sign indicating right middle lobe pneumonia. The organism is most likely to be pneumococcus, but care must be taken to consider blockage of the right middle lobe bronchus.
A 30-year-old man develops a pustular lesion at the site of a cat scratch on his forearm. This is followed 1 week later by malaise, fever, and lymphadenopathy. On examination, he has tender axillary lymph nodes. Which of the following is the most likely causative organism?
The cause of cat-scratch fever is a tiny Gram-negative bacillus, B. henselae. Cats acquire the organism from the soil and inoculate humans via scratches or bites. The disease is generally benign and self-limited, and is treated with analgesics and antipyretics. Encephalitis, seizures, coma, meningitis, and transverse myelitis can occasionally occur even in immunocompetent patients. A variety of antibiotics have been used when severe disease is present but an optimal regimen has not been identified.
A 7-year-old child, unvaccinated because of his parents’ religious beliefs, develops malaise, cough, coryza, and conjunctivitis with a high fever. Examination of his mouth reveals blue white spots on a red base beside his second molars. The next day he develops an erythematous, nonpruritic, maculopapular rash at his hairline and behind his ears, which spreads over his body. Which of the following is the most likely diagnosis?
This is a typical case of measles. The Koplik’s spots in the mouth are easily missed with poor illumination. They are white blue spots of 1 mm on a red background and are not seen in any other infectious disease. The rash of measles becomes confluent while that of rubella does not. Pneumonia is an infrequent complication but accounts for many measles deaths. Giant cell pneumonia is also seen, most commonly in children suffering with a severe disease such as leukemia or immunodeficiency. Aerosolized ribavirin has been used to treat severe pneumonia secondary to measles, but its efficacy is still unclear. The other potentially lethal complication of measles is encephalitis
A 60-year-old man presents with fever and malaise 6 weeks after mitral valve replacement. On examination, his temperature is 38C, blood pressure 130/80 mm Hg, pulse 80/min, and a loud pansystolic murmur at the apex, which radiates to the axilla. He has no skin or neurologic findings. Which of the following is the most likely causative organism?
About half of all early-onset (<60 days after surgery) prosthetic endocarditis is caused by staphylococcal infection, with S. epidermidis predominating. Early-onset prosthetic endocarditis is generally the result of intraoperative contamination of the prosthesis or a bacteremic postoperative complication.
A 73-year-old man from a nursing home develops headache, fever, cough, sore throat, malaise, and severe myalgia during a community outbreak affecting numerous other residents at the home. The symptoms gradually resolve after 3 days, and he starts feeling better but then there is a reappearance of his fever, with cough and yellow sputum production. On examination, his temperature is 38.5C, pulse 100/min, respiration 24/min, oxygen saturation 88% and crackles in the right lower lung base, bronchial breath sounds and dullness on percussion. CXR reveals a new infiltrate in the right lower lobe. Which of the following is the most likely causative organism?
This man has a complication of viral influenza; a secondary bacterial pneumonia has developed. This usually occurs 2–3 days after the initial viral symptoms resolve. Primary viral pneumonia with influenza is not common. S. pneumoniae, Staphylococcus, and H. influenzae are the most common bacterial invaders in pulmonary complications of influenza. Pneumonia is the leading cause of death and may also be due to S. pneumoniae and H. influenzae. Mixed viral and bacterial pneumonia is common; pure viral pneumonia in influenza is uncommon (but can be very severe).
A 56-year-old man is having intermittent fevers and malaise for the past 2 weeks. He has no other localizing symptoms. Two months ago, he had valve replacement surgery for a bicuspid aortic valve. Amechanical valve was inserted and his postoperative course was uncomplicated. On examination, his temperature is 38C, blood pressure 124/80 mm Hg, pulse 72/min, and head and neck are normal. There is a 3/6 systolic ejection murmur, the second heart sound is mechanical, and a 2/6 early diastolic murmur is heard. The lungs are clear and the skin examination is normal. Three sets of blood cultures are drawn and an urgent echocardiogram is ordered. Which of the following is the most likely causative organism?
S. epidermidis is still the leading cause of prosthetic valve endocarditis in the early postoperative period (usually defined <2 months). It is usually the consequence of intraoperative contamination or postoperative bacteremia. Endocarditis occurring 12 months after surgery is usually due to the same organisms that cause native valve endocarditis.
Two students from a university dormitory building have contracted meningitis due to Neisseria meningitides. Which of the following students in the dormitory are most likely to benefit from chemoprophylaxis?
Although only close contacts need chemoprophylaxis, it is sometimes given more widely than recommended because of community concern. Meningococcal vaccine is effective against serotype A and C, and will prevent late secondary infection in close contacts. Ciprofloxacin or ofloxacin are alternatives to rifampin.
A 21-year-old woman visits her physician because of 3 weeks of a “flu-like” illness. She reports symptoms of malaise, fever, fatigue, and a sore throat. There is no weight loss or night sweats, and she has not traveled out of country. Her past medical history is not significant and she is not taking any medications. Physical examination is normal except for enlarged cervical lymph nodes. Laboratory data show hemoglobin 13.2 g/dL; hematocrit 42%; platelets 380,000/mL; WBC 8500/mL, with 35% segmented neutrophils, 1% eosinophils, and 64% lymphocytes, of which 36% were atypical. A heterophil antibody (sheep cell agglutination) test is negative. Which of the following is the most likely causative organism?
The most common cause of non-EBV mononucleosis-type syndrome is CMV. It is the most common presentation of CMV in nonneonates with normal immune function.
A 23-year-old woman visits your office because of headache, malaise, anorexia, pain in both sides of her jaw, and discomfort in both lower abdominal quadrants. Physical examination reveals enlarged parotid glands; bilateral lower quadrant abdominal tenderness; a temperature of 38.7°C; and a pulse rate of 92/min. Serologic testing (IgM) confirms the diagnosis of mumps. Which of the following is the most appropriate treatment for this condition?
Antibiotics, sulfas, steroids, and mumps convalescent sera are of no value. Mouth care, analgesics, and a bland diet are usually recommended. Glucocorticoids are usually prescribed for orchitis, although definite evidence of their effectiveness is lacking. Prevention via vaccination is the preferred strategy for mumps.
A 10-year-old boy presents with fever, headache, photophobia, and neck discomfort in the middle of summer. He is alert and oriented, but has neck pain with flexion and extension of the head. His fundi are normal, and there are no focal neurologic findings or skin changes. A lumbar puncture reveals normal protein and glucose with a cell count of 240/mL (90% lymphocytes). Which of the following is the most likely causative organism?
The cerebrospinal fluid (CSF) picture in this individual is consistent with viral meningitis rather than a bacterial process. Enteroviruses are a prominent cause of viral meningitis in the summer and fall months. They received their name because they multiply in the GI tract. Fever, sometimes associated with respiratory symptoms, is the most common sequela of enterovirus infection. There are about 70 enteroviruses that affect humans. These include polioviruses, coxsackieviruses, echoviruses, and others. The spectrum of disease includes paralytic disease, encephalitis, aseptic meningitis, pleurodynia, exanthems, pericarditis, myocarditis, and nonspecific febrile illnesses. They can on occasion cause fulminant disease in a newborn. The most important enteroviruses are the three poliovirus serotypes.
An 18-year-old woman has eaten homemade preserves. Eighteen hours later, she develops diplopia, dysarthria, and dysphagia. Which of the following is the most likely causative organism?
The incubation period of C. botulinum toxin is 18–36 hours but ranges from a few hours to days. There are no sensory symptoms. Foodborne botulinum is associated primarily with home-canned food. Severe foodborne botulinum can produce diplopia, dysarthria, and dysphagia; weakness then can progress rapidly to involve the neck, arms, thorax, and legs. There is usually no fever. Nausea, vomiting, and abdominal pain can precede the paralysis or come afterward.
A previously healthy 19-year-old female university student develops myalgia, headache, fever, and malaise. Blood tests reveal lymphocytosis, with 20% of the lymphocytes being atypical. She remains tired and unwell for 6 weeks, but repeated tests for heterophil antibody are negative. Which of the following is the most likely diagnosis?
Heterophil antibody-negative mononucleosis syndrome is the most common manifestation of CMV infection in immunocompetent adults and is more common than the similar syndrome caused by toxoplasmosis. As of yet, no syndromes caused by HHV-7 have been identified in adults.
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