The Microbiology of Urinary Tract Infection among Older Adults
The most common organisms causing bacteriuria (in the general population and in older adults) are in the family Enterobacteriaceae ( Table 1 ).
E. coli has been well studied for its bacterial virulence factors; especially important is the enhanced ability of these bacteria to adhere to the uroepithelial cells (whether by pili, fimbriae or different types of adhesins). Other pathogens such as P. mirabilis and K. pneumoniae have shown similar virulence characteristics. Although the majority of UTIs are caused by a single organism, polymicrobial infections occur in about 10-25% of cases among older adults.[3,4,25]
Host factors—including a decrease in cellular and humoral immunities, comorbidities such as diabetes, chronic urinary tract problems leading to stasis, micturition dysfunction, and low urinary pH—probably all contribute to the increased prevalence of bacteriuria, especially in residents of LTC facilities. The presence of an indwelling catheter or other urinary device that can become colonized is also an important source of infection. The catheters can become coated with biofilm, rendering the antimicrobial agents present in the urine ineffective because of their poor capacity to kill the bacteria protected by this thick extracellular matrix.[20,25] Infection transmission from patient to patient can also occur through the hands of caregivers.
The emergence of resistant uropathogens to antimicrobials used as a first line of treatment has become an important problem. Many strains of E. coli are currently resistant to ampicillin because of beta-lactamase production. The resistance to co-trimoxazole (trimethoprim/sulfamethoxazole) has also increased; the SENTRY Antimicrobial Surveillance Program data from the year 2000 indicate that the rate of resistance to co-trimoxazole in North America is 23%. This is harmonious with the Canadian resistance data for 2001 and 2002, which show resistance in 15% of the isolates of E. coli (Bayer Pharmaceuticals, data on file). It seems that this increase of resistance is strongly associated with the extensive use of co-trimoxazole. Despite their increased use in the past decade, fluoroquinolones have retained their activity against E. coli and the other gram-negative uropathogens implicated in UTI. The TRUST surveillance study indicates that the susceptibility of E. coli to ciprofloxacin has remained high, at 94.5%, higher in fact than ampicillin (56.8%) and co-trimoxazole (76.2%). The problem of resistance is unfortunately even more acute for older adults, especially those in LTC facilities. It is due in part to the presence of pathogens, such as P. aeruginosa, that are more resistant to antimicrobials per se and to the extensive use of antimicrobials in this particular setting. Also, patients with poorer functional status are more likely to harbour resistant flora. Those patients are also the most likely to have a decreased immune response and urinary devices in place, thus increasing their chance of being exposed to antimicrobial treatment.
The prevalence of resistance in LTC facilities, as reported in 2000 by Wright et al., was much higher than in the general population. They reported a 68% resistance to co-trimoxazole and 41% resistance to fluoroquinolones, and 61% of their isolates were multidrug resistant.
In a review by Smith et al. on microbiology in LTC facilities, 43% of Staphylococcus aureus organisms were methicillin-resistant Staphylococcus aureus (MRSA), and 2% of enterococci were vancomycin-resistant enterococci (VRE). Since the gap between the reported rate of resistance in the general population and in LTC residents can be wide, clinicians should be aware of the resistance rate for common uropathogens in their own facilities.
Geriatrics and Aging. 2008;11(10):582-588. © 2008 1453987 Ontario, Ltd.
Cite this: Urinary Tract Infections in Older Adults: Current Issues and New Therapeutic Options - Medscape - Nov 01, 2008.