Cognitive impairment and infectious burden in the elderly

Infectious agents have been suspected as contributing factors to dementia, especially in Alzheimer disease. We intended to test whether viral or bacterial seropositivity is associated with cognitive impairment among home-dwelling elderly. Viral burden (seropositivity for herpes simplex type 1 (HSV1), type 2 (HSV2), or cytomegalovirus (CMV), and bacterial burden (Chlamydia pneumoniae and Mycoplasma pneumoniae) were tested among 383 home-dwelling individuals with vascular disease (mainly coronary heart disease) in the ongoing DEBATE study (mean age 80 years). Mini-mental state examination (MMSE) and its changes were used to define cognitive impairment. At baseline, 0-1, 2, and 3 positive titers toward viruses were found in 48 (12.5 %), 229 (59.8 %), and 106 (27.7 %) individuals, respectively. MMSE points decreased with increasing viral burden (p = 0.03). At baseline, 58 individuals (15.1 %) had cognitive impairment (MMSE < 24 points) which after adjustments was significantly associated with seropositivity for 3 viruses (risk ratio 2.5, 95 % confidence interval 1.3 to 4.7). MMSE score decreased in 150 cases (43 %) during 12-month follow-up. After adjustment for MMSE score at baseline and with 0-1 seropositivities as reference (1.0), the risk ratios were 1.8 (95 % confidence interval 0.9 to 3.6) and 2.3 (95 % confidence interval. 1.1 to 5.0) for 2 and 3 seropositivities, respectively. No significant associations were observed between bacterial burden and cognition. Viral burden of herpesvirus and cytomegalovirus was associated with cognitive impairment in home-dwelling elderly. The association may offer a preventable cause of cognitive decline.