An 83-year-old woman is brought to the emergency department from a nursing home with fever and altered mental status. The patient has a history of hypertension, dementia, and fecal incontinence. Her temperature is 38.3 C (100.9 F), blood pressure is 100/68 mm Hg, and pulse is 114/min. She is lethargic and unable to answer questions. Her abdomen is soft, with suprapubic tenderness. Lungs are clear bilaterally. There is no cardiac murmur or skin rash. Laboratory results are as follows: A chest x-ray reveals normal-appearing lungs. Blood and urine cultures are performed, and empiric antibiotics are initiated. Urine cultures grow gram-negative rods that are lactose-fermenting and indole-positive. Which of the following is the most likely organism causing this patient's infection?

Question

An 83-year-old woman is brought to the emergency department from a nursing home with fever and altered mental status.  The patient has a history of hypertension, dementia, and fecal incontinence.  Her temperature is 38.3 C (100.9 F), blood pressure is 100/68 mm Hg, and pulse is 114/min.  She is lethargic and unable to answer questions.  Her abdomen is soft, with suprapubic tenderness.  Lungs are clear bilaterally.  There is no cardiac murmur or skin rash.  Laboratory results are as follows:  A chest x-ray reveals normal-appearing lungs.  Blood and urine cultures are performed, and empiric antibiotics are initiated.  Urine cultures grow gram-negative rods that are lactose-fermenting and indole-positive.  Which of the following is the most likely organism causing this patient's infection?

Quizplus · Accepted Answer

11ec160b_3867_7c0a_9249_9545083f529f_MD0001_00 This patient has sepsis, most likely due to a urinary tract infection (UTI), as evidenced by the presence of pyuria (leukocytes), leukocyte esterase, and gram-negative rods in the urine. Among the organisms listed, the microbiological features - lactose-fermenting, indole-positive gram-negative rods - are characteristic of Escherichia coli, the most common etiology of UTIs among elderly women. The indole positivity (ability to convert tryptophan to indole) of E coli distinguishes it from Enterobacter cloacae, another lactose-fermenting gram-negative rod that is a common cause of UTIs in women (Choice A). Both E coli and E cloacae are fast lactose fermenters. (Choice C) Haemophilus influenzae are gram-negative organisms that colonize the respiratory tract rather than the gastrointestinal and genitourinary tracts; they do not typically cause UTIs. These organisms are frequent causes of pneumonia, sinusitis, and, less commonly, meningitis. (Choices D and E) Proteus mirabilis and Pseudomonas aeruginosa are gram-negative organisms that can cause UTI, most commonly in patients with Foley catheters. However, in contrast to E coli, these organisms are lactose non-fermenters (do not form pink colonies on MacConkey agar). Educational objective: Escherichia coli are lactose-fermenting, indole-positive gram-negative rods that are an important cause of urinary tract infection in women. __________ References: Epidemiology of urinary tract infection: transmission and risk factors, incidence, and costs. (http://www.ncbi.nlm.nih.gov/pubmed/12848468) Urinary tract infections in older women: a clinical review. (http://www.ncbi.nlm.nih.gov/pubmed/24570248)

An 83-Year-Old Woman Is Brought to the Emergency Department from a Nursing