Herpes Zoster Severity May Increase Dementia Risk in Older Adults

Greater severity of herpes zoster infection leads to an increased risk for dementia among older adults, according to study results published in The Journal of Prevention for Alzheimers Disease.

Evaluating dementia risk in the aging population is important for public health. Owing to contradictory data on the effect of herpes zoster on occurrence of dementia, researchers studied the association between severe herpes zoster infection and risk of developing dementia among patients aged 50 years and older.

Patient information, including hospital discharges and prescription medications, were collected from health records, registries, and other databases. Herpes zoster was confirmed using the International Classification of Diseases, Ninth Revision (ICD-9).

Exposure of interest was hospitalization with a diagnosis of herpes zoster and outcome of interest was incidence of dementia. Entry date was defined as date of first hospital admission with a herpes zoster diagnosis.

Participants were followed up until diagnosis of dementia, death, emigration out of study region, or end of the study period, whichever occurred first. Patients with herpes zoster (group 1) were matched 1:5 with individuals in the general population (group 2) and with patients hospitalized with other diagnoses other than herpes zoster (group 3).

For the study, the researchers extracted data from 7,030,374 adults between 2001 and 2023, of which data from 132,968 (mean age, 74.6 years; women, 57.6%) were identified for the study. Group 1 included 12,088 patients; group 2 had 60,440 individuals; and group 3 also had 60,440 patients.

The researchers reported new cases of dementia and deaths over the 23-year study period (Table 1), as well as the cumulative incidence function of dementia (Table 2).

Table 1: New cases of dementia and deaths in the study period.

Group	Dementia	Deaths
1	1606	6772
2	7636	23,505
3	7481	31,775

Table 2: Overall, 1-year, and 10-year cumulative incidence function of dementia (95% CI).

Group	Overall	1 Year	10 Year
1	17.9% (17.0%-18.8%)	19.3% (18.8%-19.7%)	17.0 (16.6%-17.5%)
2	2.9% (2.6%-3.2%)	1.1% (1.0%-1.2%)	3.0% (2.8%-3.1%)
3	11.9% (11.3%-12.6%)	10.6% (10.3%-10.8%)	11.0% (10.7%-11.3%)

The researchers also compared adjusted subdistribution hazard ratios (SHR) for dementia and herpes zoster during the follow-up period. Overall adjusted SHR of dementia was 1.13 (95% CI, 1.07-1.19) in group 1 vs group 2, and 1.08 (95% CI, 1.03-1.14) in group 1 vs group 3. Early SHR for dementia at 1 year was 2.43 (95% CI, 2.15-2.75) in group 1 vs group 2, and 0.97 (95% CI, 0.87-1.08) in group 1 vs group 3.

Results of the stratified analyses were consistent with primary results, except for patients aged between 50 and 65 years among whom the association between dementia and herpes zoster were higher (SHR, 7.54; 95% CI, 2.35-24.12). After 10 years of follow-up, SHRs of dementia were 1.22 (95% CI, 1.15-1.29) in group 1 vs group 2, and 1.08 (95% CI, 1.02-1.14) in group 1 vs group 3.

In the period between 1 and 10 years of follow-up, the researchers noted adjusted SHRs for dementia of 1.16 (95% CI, 1.09-1.24) in group 1 vs group 2, and 1.11 (95% CI, 1.04-1.19) in group 1 vs group 3. Between 10 years and the end of follow-up, adjusted SHRs were 1.27 (95% CI, 1.13-1.43) in group 1 vs group 2, and 1.24 (95% CI, 1.10-1.39) in group 1 vs group 3.

Limitations of the study included its retrospective design; excluding data from outpatient services; and lack of including confounders such as socioeconomic factors, lifestyle, and other risk factors.

“[These] results support the importance of improving zoster prevention and extending the vaccination recommendations to younger age groups,” the researchers concluded.