Infection: General Principles
This chapter addresses the following Geriatric Fellowship Curriculum Milestones: #18, #21, #29, #39, #42
Identify and address modifiable risk factors for infection in older adults.
Appropriately order and use culture data in older adults, including knowing when NOT to order cultures of urine and skin.
Identify the most common causes of fever of unknown origin (FUO) in older adults and modify the FUO work-up versus that used in young adults.
Key Clinical Points
Multiple risk factors including comorbidity, malnutrition, immune senescence, and social determinants of health (eg, nursing home residence, poor access to care) increase the risk of infection in older adults versus young adults.
Although antibiotic dose adjustments are sometimes necessary for seniors due to declines in renal or hepatic function, the adage of “start low, go slow” should NOT be used to guide initial antibiotic dosing for serious infections in older adults in whom time to effective treatment is a major determinant of outcome. Providing full initial dosing of antibiotics is critical in these situations with changes in subsequent doses to adjust for renal or hepatic function.
Because asymptomatic colonization (eg, asymptomatic bacteruria) is common in seniors, it is prudent to adopt a practice of “culture stewardship.” This concept is akin to antibiotic stewardship to reduce unnecessary antibiotic use, but avoids unnecessary antibiotics by limiting the collection of culture samples to only those clinical conditions where they are of clear benefit. Cultures should only be performed when there is strong evidence of infection (eg, new-onset fever, delirium), and never from skin surface swabs or urine in the presence of a long-term indwelling catheter; cultures in these settings are more often misleading than helpful.
The causes of FUO differ in old versus young adults most notably with temporal arteritis being the underlying diagnosis in about 1 in every 6 cases of FUO in those age 60 years and over. Temporal arteritis is absent in FUO series in adults less than 50 years of age.
PREDISPOSITION OF OLDER ADULTS TO INFECTION
A number of factors increase the risk of infection in older adults compared to young adults. The relationships between these risk factors may be very complex leading seemingly similar patients to have markedly different overall risk for clinical infection. For example, many older individuals have latent infection with Mycobacterium tuberculosis (ie, asymptomatic infection) and do not manifest clinical illness despite an aging immune system and the presence of various comorbid conditions. However, superimposing malnutrition, perhaps due to medication- or illness-induced anorexia, may be the final insult necessary to tip the scales toward illness resulting in clinical manifestations. Several well-recognized features associated with advanced age clearly increase risk for clinical infection; these are reviewed in the following paragraphs.
In older adult individuals, there is ...