In a study examining the factors that play a role in an older adult's transition to disability, intervening illnesses and injuries that led to hospitalization or activity restriction were associated with worsening functional ability, especially among those who were physically frail, according to a study in the November 3 issue of JAMA, a theme issue on aging.

Thomas M. Gill, M.D., of the Yale University School of Medicine, New Haven, Conn., presented the findings of the study at a JAMA media briefing at the National Press Club.

Among older persons, disability in essential activities of daily living, such as bathing, dressing, and walking, is common and associated with an increased rate of death, institutionalization, and greater use of formal and informal home services. However, many older persons also recover from disabilities. "Disability among older persons is a complex and highly dynamic process with high rates of recovery and frequent transitions between states of disability. The role of intervening illnesses and injuries (i.e., events) on these transitions is uncertain," according to background information in the article.

Dr. Gill and colleagues conducted a study to evaluate the association of intervening events with transitions between states of no disability, mild disability, severe disability, and death, and to determine the association of physical frailty with these transitions. The study, conducted from March 1998 to December 2008, included 754 community-living persons ages 70 years or older who were nondisabled at the beginning of the study in 4 essential activities of daily living: bathing, dressing, walking, and getting out of a chair. Of these participants, 117 (15.5 percent) remained nondisabled and alive through the end of follow-up and therefore made no transitions during a median (midpoint) follow-up of about 10 years.

Telephone interviews were completed monthly for more than 10 years to assess disability and to determine exposure to intervening events, which included illnesses and injuries leading to either hospitalization or restricted activity. Participants were assessed for physical frailty (with a rapid gait test) every 18 months, through 9 years. The primary outcomes measured included transitions between no disability, mild disability, and severe disability and 3 transitions from each of these states to death, evaluated each month.

The researchers found that among the 637 participants who had at least 1 functional transition, 578 (90.7 percent) had at least 1 hospital admission and 601 (94.3 percent) had at least 1 month of restricted activity during a median follow-up of 8.5 years. Hospitalization was associated with disability for 8 of the 9 transitions (the ninth being severe disability to no disability). "Restricted activity increased the likelihood of transitioning from no disability to both mild and severe disability, respectively, and from mild disability to severe disability, but was not associated with recovery from mild or severe disability," the authors write. Overall, the association of hospitalization with the disability transitions was much more pronounced than the association of restricted activity with disability transitions.

The researchers add that regardless of intervening event, the absolute risk of transitions to new or worsening disability or death was consistently higher in participants with frailty, while transitions representing functional recovery were consistently more likely in those who were not frail. "For example, the absolute risk of transitioning from no disability to mild disability within 1 month after hospitalization for frail individuals was 34.9 percent vs. 4.9 percent for non-frail individuals."

Among the possible reasons for hospitalization or restricted activity, fall-related injury conferred the highest likelihood of developing new or worsening disability.

"Despite the reductions observed in the prevalence of disability over the past 2 decades, the absolute number of disabled older Americans could increase substantially in the coming years with the aging of the baby boom generation. To obviate this increase, more aggressive efforts will be needed to prevent and manage intervening illnesses and injuries, given their apparent role in precipitating and perpetuating the disabling process," the authors conclude.