MR. STEIN, 71, is confined to a wheelchair in a long-term-care (LTC) facility. Twice in the last 24 hours he's found lying on the floor. He didn't sustain any injuries, he denies pain or discomfort, and his vital signs are stable. However, he's had an acute change in mentation, and is now incontinent of both urine and feces. The staff suspects an infection.
Older adults like Mr. Stein are at risk for potentially life-threatening infections due to age-related physiologic changes in the immune, respiratory, urinary, and gastrointestinal systems. The risk increases in those with comorbid diseases, functional impairment, malnutrition, hospitalization, and invasive devices.1,2
This article focuses on assessment and interventions for Salmonella arizonae, an uncommon but potentially serious cause of urinary tract infection (UTI).
Acute functional changes
As in Mr. Stein's case, an acute change in functional or cognitive status may indicate infection. Older adults may not present with classic UTI signs and symptoms (frequency, urgency, dysuria, nocturia, suprapubic discomfort, hematuria). Up to 33% of older adults may have an acute infection without fever.2
Specimens for urinalysis (UA) and urine culture and sensitivity are obtained. Mr. Stein's UA is remarkable for haziness (normal is clear), positive for 2+ leukocyte esterase (normal is negative), and positive for nitrites (normal is negative). The urine culture is positive for S. arizonae. The lab notifies the local Department of Health because Salmonella is a reportable disease-producing organism.
Common infection, uncommon cause
UTI is the most common bacterial infection in older adults, with a higher frequency among older women than men.3 Cloudy urine may be caused by the presence of white blood cells (WBCs) or bacteria. The urine leukocyte esterase test detects the presence of esterase released by WBCs and is elevated in bacterial, fungal, and parasitic infections. Many Gram-negative organisms, including salmonella, produce enzymes that reduce urinary nitrate to nitrite. A positive nitrite test is a reliable indicator of significant bacteriuria.4
An uncommon human pathogen, S. arizonae was first identified in Arizona in 1939.5 Reptiles, particularly snakes, are asymptomatic reservoirs for this organism.
Most S. arizonae cases have been reported in the southwestern United States because of a large Hispanic population that uses rattlesnake products for medicinal purposes.5 But infection can also be found beyond the southwest and may not be associated with exposure to snakes and reptiles.
Serious S. arizonae infections have been reported in immunocompromised patients such as those with HIV infection, conditions requiring immunosuppressive therapy, and children under age 7.5 In addition, older adults like Mr. Stein experience a diminished immune response, including changes in cell-mediated and humoral immune responses, making them more susceptible to infections. Isolation of this organism from blood, tissue, or normally sterile body sites should raise suspicions of an immunocompromised state because S. arizonae infection hasn't been documented in a healthy human adult.5
Treating the infection
There's no standard therapy for S. arizonae UTI, but the organism is susceptible to commonly prescribed antibiotics, including ampicillin and fluoroquinolones.5
Culture-drug sensitivities reveal the organism is sensitive to fluoroquinolones, and oral ciprofloxacin is ordered for 10 days. Mr. Stein remains clinically stable. The ciprofloxacin is well tolerated and his mentation and behavior return to baseline.
Because older patients are predisposed to infectious diseases due to age-related physiologic changes, they may present with atypical signs and symptoms. A thorough physical assessment and careful interpretation of laboratory findings will lead to prompt and appropriate treatment.
1. Arinzon A, Peisakh A, Shuval I, Shabat S, Berner Y. Detection of urinary tract infection in long-term care setting: is the multireagent strip an adequate diagnostic tool? Arch Gerontol Geriatr
2. Norman DC. Fever in the elderly. Clin Infect Dis
3. Nicolle LE. Urinary tract infections in the elderly. Clin Geriatr Med
4. Fischbach F. A Manual of Laboratory & Diagnostic Tests
, 7th ed. Philadelphia, Pa.: Lippincott Williams & Wilkins; 2004.
5. Hoag JB, Sessler CN. A comprehensive review of disseminated Salmonella arizona
infection with an illustrative case. South Med J