Infectious Disease Exam Master 2024 Questions With Complete Answers Graded A+

Case A 2-year-old girl presents with a fever and an inflamed throat. Her mother states the child does not want to eat. You decide to treat her with 7 days of penicillin. After 4 days, the mother calls your office to report that the child has not significantly improved. You suspect the child's infection may be caused by penicillin-resistant bacteria. Question What is the likely mechanism of resistance in this case? - CORRECT ANSWER Correct answer: Acquisition of the enzyme β-lactamase Explanation Bacteria carrying a plasmid with the gene for β-lactamase would confer resistance to antibiotics containing the β-lactam ring, such as penicillin and amoxicillin. β-Lactamase is an enzyme that cleaves and inactivates antibiotics like penicillin. The antibiotic penicillin consists of a thiazolidine ring fused to a β-lactam ring (see image). A variable "R" group is attached to the β-lactam ring by a peptide bond. Penicillin inhibits bacterial cell growth by inhibiting the enzyme catalyzing the last step in cell wall synthesis. This step involves the cross-linking of the peptidoglycan strands. Under normal conditions, a peptide bond forms between the terminal glycine on one proteoglycan strand, with the terminal D-Ala-D-Ala unit on the other strand forming the Gly-D-Ala cross-link. The enzyme catalyzing this reaction is glycopeptide transpeptidase. Penicillin inhibits this reaction by mimicking the D-Ala-D-Ala unit, forming a covalent bond between the R-group of penicillin and the active site serine of glycopeptide transpeptidase. The penicilloyl-enzyme complex is enzymatically inactive; therefore, penicillin acts as a transition state analog. Bacterial plasmids often carry genes that confer resistance to a specific antibiotic. Other examples of enzymes carried on plasmids that convey antibiotic resistances are chloramphenicol acetyltransferase, which inactivates chloramphenicol, and phosphotransferases, which modify aminoglycosides such as neomycin and gentamicin. These plasmids can be passed from a resistant to a sensitive bacterial cell, conveying resistance to a particular antibiotic; therefore, many strains of resistant bacteria have arisen, which cause problems in treating the patient. Resistance to penicillin is not due to mutations in the Case A healthy couple presents for an evaluation prior to travel to the Dominican Republic; they leave in 1 month and will stay there 4 weeks. The CDC lists the Dominican Republic as a malaria-endemic area, but it is not considered to have a resistant strain of Plasmodium falciparum. Question What is the best advice for this couple? - CORRECT ANSWER Correct answer: "You should both take chloroquine weekly starting 1 week before travel." Explanation When there is no drug resistance to Plasmodium falciparum (one of the Plasmodium protozoans that causes malaria), weekly chloroquine is the prophylactic drug of choice. It is well-tolerated and can be dosed once weekly rather than daily (hydroxychloroquine is similar for malaria prophylaxis). Travelers should be advised of the risk of malaria, chemoprophylaxis, and personal protection measures. The chloroquine should be dosed weekly starting 1-2 weeks prior to travel, continuing throughout travel, and discontinued 4 weeks after return from a malaria-endemic region. Atovaquone/proguanil, mefloquine, doxycycline, and primaquine can be considered for regions known to have resistant strains of P. falciparum. P. falciparum can be transmitted via mosquito bites. The risk of malaria infection rises with the number of mosquito bites, but the bite alone does not guarantee malaria, even in endemic regions. The couple should be educated on mosquito bite prevention for their travel. Malaria can be effectively treated in most countries, and patients should also be educated on when and how to seek care when traveling abroad. Malaria typically causes an influenza-like illness, with fevers, chills, malaise, headaches, and myalgias. Severe cases can progress to seizures and death. Prophylaxis, prompt evaluation, and treatment of malaria are essential for travelers. Malaria chemoprophylaxis should continue for 7 days to 4 weeks after return from travel. Continuation of treatment for 4 weeks post-return is recommended when using chloroquine, mefloquine, and doxycycline for malarial prophylaxis, and 7 days when using atovaquone/proguanil. While self-treatment is not ideal, the CDC recommends the use of atovaquone/proguanil (Malarone Case A 23-year-old man presents with a 2-day history of watery nasal discharge, malaise, sneezing, and nasal congestion. On examination, you notice inflammation of the nasal mucosa. Pulse is 80/min. BP is 130/80 mm Hg, and temperature is 98.8 °F. Question What investigations will you order to establish the diagnosis? - CORRECT ANSWER Correct answer: No specific diagnostic workup needed Explanation The correct answer is no specific diagnostic workup needed. This patient is suffering from viral rhinitis (common cold). No specific workup beyond a clinical diagnosis is necessary for an otherwise healthy patient1. Nasal swab with polymerase chain reaction PCR can help establish a specific viral etiology, if needed. Complete blood count may show increased total leukocyte count. Viral serology establishes a specific viral etiology. X-rays may be positive in cases of sinus involvement. These investigations are not done routinely to establish a diagnosis, but may be necessary in specific clinical scenarios, such as in patients who are immunocompromised. Case An 18-month-old infant presents with a 5-day history of fever of 104°F. On physical examination, you note a mildly lethargic and irritable infant. There are no other clinically significant findings. You prescribe acetaminophen (Children's Tylenol) and tell the mother to monitor the infant's fever for the next few days; if the fever goes down, everything should be fine. The mother calls the next day and says that the fever has stopped, but a rash has developed and she is concerned. The infant examination reveals a diffuse, fine, maculopapular rash. Presently, the child does not appear ill. Question What is the most likely diagnosis? - CORRECT ANSWER Correct answer: Roseola Explanation The clinical picture is suggestive of roseola. Roseola is a benign illness in humans caused by the human herpesvirus 6 or 7. It is the major cause of acute febrile illness in young children. The most prominent feature is a fever lasting up to 8 days, the fever often exceeding 39.5°C (103.1°F). After the fever subsides, a rose-pink maculopapular rash appears. Rubella appears as a maculopapular rash beginning on the face and spreading to the entire body; it disappears by the fourth day after prodrome of low-grade fever, ocular pain, sore throat, and myalgias. Rubeola consists of the prodrome of fever, cough, conjunctivitis, and coryza. The rash appears as maculopapular, spreading down from the face and hairline to the trunk over 3 days, then becoming confluent. Erythema infectiosum rash appears as raised, fiery-red maculopapular lesions on the cheeks that give a "slapped-cheek" appearance. Varicella (chickenpox) rash appears as widely scattered red macules and papules concentrated on the trunk and face, progressing to vesicles and pustules and followed by crusting of the lesions. Case A 24-year-old man with a past medical history of HIV positive status for 2 years presents due to an ongoing chronic cough that he has had for the past 8 months. He admits to a mild fever that comes and goes during that same time period. A 5-pound unintentional weight loss is also discovered since his last visit to your office, which was approximately 9 months ago. He states he has noted an increased amount of breathlessness with just simple activities, which was never bothersome before the cough began. The patient denies smoking, and his TB test is negative. Question What is the most likely organism causing this patient's signs and symptoms? - CORRECT ANSWER Correct answer: