Trends in encephalitis-associated deaths in the United States

Abstract

The United States national mortality statistics and HIV/AIDS surveillance data were analysed to determine trends in encephalitis-associated deaths and to assess the impact of HIV infection on those deaths during 1979-1998, a period when ICD-9 codes were used for coding deaths in the United States. A total of 25125 encephalitis deaths were reported; 4779 of them (19%) had concurrent HIV infection. Overall encephalitis death rates remained stable, but they increased for groups where HIV infection was common and declined or remained unchanged for others. For persons without HIV infection, the rates declined in all demographic groups. Encephalitis deaths in HIV-infected persons followed general trends for HIV deaths in the United States. The rates in the HIV-infected population were several hundred- to thousand-fold higher than in the HIV-uninfected population. HIV infection was largely responsible for the lack of overall decline in the considerable mortality associated with encephalitis in the United States during 1979-1998.

Trends in Encephalitis-Associated Deaths in the United States, 1999-2008

“…This study found that the downward trend noted during 1989-1998 in the US encephalitis-associated death rate continued through 1999-2008 [8]. The only annual rate increase identified during the study period was from 2001 to 2002, which corresponds to the introduction of WNV into the USA, and primarily affected the ≥65-year age group [23,24].…”

“…Cause-of-death information is coded from a specific section on death certificates completed by the person certifying the death. The ICD-10 codes used to identify encephalitis-associated deaths were selected to be consistent with ICD-9 codes from previous encephalitis mortality studies (table 1) [7,8]. Encephalitis deaths were categorized into two groups: ‘specified encephalitis' using the specified encephalitis causes (ICD-10 codes) and ‘unspecified encephalitis' which included the remaining encephalitis death records (table 1) [15].…”

“…Despite extensive laboratory diagnostic testing for infectious or other etiologies of encephalitis, the underlying cause often remains unknown [6]. Previous studies in North America, Europe and Australia have estimated the encephalitis incidence between 3.4 and 7.4 per 100,000 patient-years with up to 86% of cases attributed to an unknown cause [2,7,8,9,10]. …”

“…In the USA, the rate of encephalitis-associated deaths based on multiple cause-of-death mortality data was stable at approximately 5.1 and 5.3 per 1 million population for 1979-1988 and 1989-1998, respectively [8]. However, significant differences in encephalitis death rate trends among persons with and without human immunodeficiency virus (HIV) were identified; the rate for non-HIV encephalitis-associated deaths declined in all categories while the rate for encephalitis-associated deaths among HIV-positive persons increased.…”

“…In Australia, where similar studies were conducted, the rate of encephalitis deaths was 2.3 per 1 million persons for 1979-2006 with an average annual decline of 2.3%, primarily associated with identified causes [7]. This Australian assessment was based on encephalitis as the primary cause-of-death, whereas the US study reported multiple cause-of-death mortality, which presumably contributes to the lower rate reported in Australia [7,8]. …”