Comorbidities, metabolic changes make elderly more susceptible to infection

In this Ask the Experts feature, Infectious Disease News Editorial Board member Keith S. Kaye, MD, discusses the special considerations when treating infections in the elderly.

Issue: September 2011

Are the elderly more susceptible to infections?

Older adults become more susceptible to infections due to several factors. As people get older, it is more frequent that they have comorbid conditions, such as diabetes, renal insufficiency and arthritis. Many comorbid conditions, both the number and type of comorbid conditions, predispose people to infections. Often, when people age, there is immunosenescence, which means that the immune system doesn’t function as well or as vigorously. The combination of increased comorbid conditions and the decrease in activity of the immune system can make people more prone to infections. The other syndrome that occurs when people become old is frailty. When people become frail, their body mass index drops and they have a harder time functioning independently, in terms of their daily living activities. They become more prone to falls and injuries. All of these things predispose older people to infections. There is an increased association with being older and an increased risk of infection, but it probably has more to do with how successfully some people age. Some people age and they remain active and healthy, and individuals such as that probably do not have an increased risk of infections. But individuals who become frailer and more dependent on others for maintaining their health status and their daily activities, their risk for infections increases greatly.

Keith S. Kaye, MD

Are infections in the elderly more common in places such as nursing homes, or are they prevalent in the entire elderly population?

What you start seeing is that people who need a lot of assistance or have comorbid conditions are more likely to end up in assisted living facilities or nursing homes. So, some of the highest-risk older adults are in nursing homes. I do think that there is an association between increased age in general and infection risk. You have to be careful not to lump all older adults into one single category. Older people in general may be at increased risk for infection, but there are certainly subsets of older adults, some of whom that are at increased risk and some of whom really are not.

What special considerations are there when treating infections in the elderly?

Treating infections in older adults is a special niche. One thing that needs to be considered is the side effects and tolerability of the medications. Sometimes, in older adults, their metabolism and their clearance of medications changes as they get older. Also, they are often on other medications. Sometimes, they can be susceptible to side effects of medications, so the side effect profile of medications must be taken into account when treating infections in the elderly. You want to take into account the other medications they are taking and also their renal function and how well you dose the medication. Other side effects of antibiotics include Clostridium difficile, which ironically, is caused by antibiotic use. We used to think that antibiotics were harmless. If there is any concern about whether or not people might have an infection, particularly those adults who are in institutions such as nursing homes, we need to be more thoughtful about who really needs antibiotics. It used to be that if a patient had a positive culture in their urine, you treated it regardless. But now, we have to think about whether someone truly has an infection or is just colonized, as antibiotics use can lead to superinfections.

What are some of the best ways to prevent infections in the elderly?

There are a few different ways. One is vaccination. We have a good vaccine program nationally, but our vaccination rates are suboptimal for a developed country such as the US. Yearly influenza vaccinations are necessary. Influenza not only causes the flu, but in older adults particularly, it causes superinfections with bacterial pneumonia. Getting the flu vaccine and making sure that older adults are up-to-date on their pneumococcal vaccination are important. In institutional settings, such as in hospitals and nursing homes, good hand hygiene by staff and avoiding the spread of pathogens from one patient to another is important. The final thing is for older adults to stay active. The longer they can remain independent and function without needing hands-on assistance or needing feeding tubes or urinary catheters will decrease the risk of infections, as well.

Is it difficult to diagnose infections in the elderly?

Infections in the elderly can present in atypical ways. A lot of times, older adults may not have a fever as readily as individuals who are younger. The fever may be lower grade. Sometimes, signs of infections might be a change in mental status or poorer functioning. Things such as the cough associated with pneumonia may not be as recognizable. The other issue with older adults, particularly when there is dementia or other comorbid conditions that may interfere with the accuracy or ability to interpret their history, you can’t get a good history of what hurts or what is bothering them. It can be a challenge to figure out if they have an infection or to determine what type of infection they have. Sometimes, standard tests such as chest X-rays might initially not be positive because the patient is dehydrated and pneumonia can’t be seen. This can be confusing. Once individuals are hydrated or in the hospital for a while, things may become more obvious. So symptoms can be atypical and underwhelming; also, the history can be difficult to elicit and some tests such as X-rays may not be as sensitive to detect abnormalities in older adults. – by Emily Shafer

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