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Encephalitis produces considerable morbidity in the United States, but morbidity rates among American Indian/Alaska Native (AI/AN) people have not been described. Hospitalization records listing an encephalitis diagnosis were analyzed by using Indian Health Service direct/contract inpatient data. For 1998–2010, there were 436 encephalitis-associated hospitalizations among AI/AN people, an average annual age-adjusted hospitalization rate of 3.1/100,000 population. The rate for infants (11.9) was more than double that for any other age group. Death occurred for 4.1% of hospitalizations. Consistent with reports for the general U.S. population, the rate was high among infants and most (53.9%) hospitalizations were of unexplained etiology. The average annual rate during the study period appeared lower than for the general U.S. population, due particularly to lower rates in the elderly. Future community-based surveillance and mortality studies are needed to confirm these findings and examine reasons underlying the low rates of encephalitis in AI/AN people.

To examine trends of Rocky Mountain spotted fever (RMSF) incidence among American Indians compared with other race groups, a retrospective analysis of national RMSF surveillance data reported to the National Electronic Telecommunications System for Surveillance and the Tickborne Rickettsial Disease Case Report Forms system were used. The RMSF incidence for American Indians, which was comparable to those for other race groups during 1990-2000, increased at a disproportionate rate during 2001-2005. The average annual incidence of RMSF reported among American Indians for 2001-2005 was 16.8 per 1,000,000 persons compared with 4.2, 2.6, and 0.5 for white, black, and Asian/Pacific Islander persons, respectively. Most cases in American Indians were reported from Oklahoma (113.1 cases per 1,000,000), North Carolina (60.0), and Arizona (17.2). The incidence of RMSF increased dramatically among American Indians disproportionately to trends for other race groups. Education about tick-borne disease and prevention measures should be addressed for high-risk American Indian populations.

To describe the epidemiology of ulcers, gastric cancer, and Helicobacter pylori infection among American Indian (AI) and Alaska Native (AN) persons, we analyzed hospitalization discharge records with physician discharge diagnoses coded as ulcer, gastric cancer, and mucosa-associated lymphoid tissue (MALT) lymphoma during 1980 to 2005, and H. pylori during 1996 to 2005 from the Indian Health Service Inpatient Dataset. The average annual age-adjusted rate of hospitalizations that included an ulcer-associated condition was 232.4 per 100,000 AI/AN persons. The age-adjusted rate for gastric cancer was 14.2 per 100,000 persons. MALT lymphoma was listed as a discharge diagnosis at an age-adjusted rate of 6.1 per 100,000, and the age-adjusted rate of H. pylori discharge diagnoses was 28.2 per 100,000. The AI/AN persons living in the Alaska region and those ≥ 65 years old had the highest rates of hospitalizations that listed ulcer-associated conditions, gastric cancers, MALT lymphoma, and H. pylori as a discharge diagnosis.

Plague and hantavirus pulmonary syndrome (HPS) are severe, often fatal diseases in humans that share a broad epidemiologic focus in the southwestern United States. Prevention of these diseases relies heavily on education and reducing rodent abundance in peridomestic environments. Resources for these activities are limited. Therefore, identifying areas sharing elevated risk for these two relatively rare but severe diseases could be useful for targeting limited public health resources. Using logistic regression and geographic information system-based modeling, we identified environmental predictors of elevated risk for plague (distance to pinon-juniper ecotones and amount of precipitation) and HPS (elevation and amount of precipitation) in northeastern Arizona and northwestern New Mexico. Our models accurately identified case locations as suitable (producer accuracies of 93% for plague and 96% for HPS) and indicated that approximately half of the coverage area was classified as suitable risk for either plague or HPS. The probability of a site being classified as suitable for plague was strongly correlated with its probability of being classified as suitable for HPS (rhos = 0.88). Increased risk for both diseases occurred for approximately 37% of the coverage area.

Yersinia pestis, the causative agent of plague, has been detected in fleas and mammals throughout the western United States. This highly virulent infection is rare in humans, surveillance of the disease is expensive, and it often was assumed that risk of exposure to Y. pestis is high in most of the western United States. For these reasons, some local health departments in these plague-affected regions have hesitated to undertake surveillance and other prevention activities. To aid in targeting limited public health resources, we created a fine-resolution human plague risk map for New Mexico, the state reporting more than half the human cases in the United States. Our GIS-based model included three landscape features—a nonlinear relationship with elevation, distance to water, and distance to the ecotone between Rocky Mountain/Great Basin open and closed coniferous woodlands—and yielded an overall accuracy of ≈ 80%. The model classified 17.25% of the state as posing significant risk of exposure to humans on privately or tribally owned land, which suggests that resource requirements for regular surveillance and control of plague could be effectively focused on < 20% of the state.

To describe the epidemiology of Rocky Mountain spotted fever (RMSF) among American Indians/Alaska Natives (AI/ANs), we conducted a retrospective analysis of hospitalization records with an RMSF diagnosis using Indian Health Service (IHS) hospital discharge data for calendar years 1980-2003. A total of 261 RMSF hospitalizations were reported among AIs, for an average annual hospitalization rate of 1.21 per 100,000 persons; two deaths were reported (0.8%). Most hospitalizations (88.5%) occurred in the Southern Plains region, where the rate was 4.23 per 100,000 persons. Children 1-4 years of age had the highest age-specific hospitalization rate of 2.50 per 100,000 persons. The overall annual RMSF hospitalization rate declined during the study period. Understanding the epidemiology of RMSF among AI/ANs and educating IHS/tribal physicians on the diagnosis of tick-borne diseases remain important for the prompt treatment of RMSF and the reduction of the disease occurrence among AI/ANs, particularly in high-risk areas.

The relationships between climatic variables and the frequency of human plague cases (1960-1997) were modeled by Poisson regression for two adjoining regions in northeastern Arizona and northwestern New Mexico. Model outputs closely agreed with the numbers of cases actually observed, suggesting that temporal variations in plague risk can be estimated by monitoring key climatic variables, most notably maximum daily summer temperature values and time-lagged (1 and 2 year) amounts of late winter (February-March) precipitation. Significant effects also were observed for time-lagged (1 year) summer precipitation in the Arizona model. Increased precipitation during specific periods resulted in increased numbers of expected cases in both regions, as did the number of days above certain lower thresholds for maximum daily summer temperatures (80 degrees F in New Mexico and 85 degrees F in Arizona). The number of days above certain high-threshold temperatures exerted a strongly negative influence on the numbers of expected cases in both the Arizona and New Mexico models (95 degrees F and 90 degrees F, respectively). The climatic variables found to be important in our models are those that would be expected to influence strongly the population dynamics of the rodent hosts and flea vectors of plague.

During an outbreak of hantavirus pulmonary syndrome (HPS) in the southwestern United States, trained environmental assessment teams conducted surveys at 17 case-patient homes and matched controls from June through August 1993. Variables related to rodent abundance were quantified and standardized rodent trapping was conducted around and within households. The majority of households were located in pinon-juniper vegetation zones, and there were no significant differences in the type of house in which cases and controls lived. The only environmental factor that distinguished case households from controls was significantly higher small rodent densities (median trap success for case sites = 17.3%, 12.7% for near controls, and 8.3% for far controls). Frequency of hantaviral infection in deer mice (Peromyscus maniculatus) did not vary significantly among households of cases and controls, with a range of 27.5-32.5% antibody-positive. Indices of rodent fecal contamination were slightly higher in case houses. The data indicate that higher rodent densities were associated with households in which HPS cases occurred. Strategies that control rodent numbers and decrease rodent access to dwellings may reduce risk of human infection.

Ehrlichiosis and anaplasmosis infections among American Indians (AIs) have never been specifically examined, despite high rates of other tick-borne rickettsial diseases among AIs. The epidemiology of ehrlichiosis and anaplasmosis among AIs was analyzed using the National Electronic Telecommunications System for Surveillance (NETSS), Case Report Forms (CRFs), and Indian Health Service (IHS) inpatient and outpatient visits. The 2000-2007 average annual ehrlichiosis and anaplasmosis incidence among AIs reported to NETSS was almost 4-fold lower (4.0/1,000,000) than that using IHS data (14.9). American Indian cases reported from CRFs had a higher proportion of hospitalization (44%) compared with IHS (10%). American Indian incidence of ehrlichiosis and anaplasmosis was higher and showed a different age and geographical distribution than other races. These results highlight the need to improve collaboration between the ehrlichiosis and anaplasmosis surveillance systems for AIs so as to develop interventions that target the unique epidemiology and mitigate the burden of disease among this high-risk population.

American Indians are at greater risk for Rocky Mountain spotted fever (RMSF) than the general U.S. population. The epidemiology of RMSF among American Indians was examined by using Indian Health Service inpatient and outpatient records with an RMSF International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis. For 2001–2008, 958 American Indian patients with clinical diagnoses of RMSF were reported. The average annual RMSF incidence was 94.6 per 1,000,000 persons, with a significant increasing incidence trend from 24.2 in 2001 to 139.4 in 2008 (P = 0.006). Most (89%) RMSF hospital visits occurred in the Southern Plains and Southwest regions, where the average annual incidence rates were 277.2 and 49.4, respectively. Only the Southwest region had a significant increasing incidence trend (P = 0.005), likely linked to the emergence of brown dog ticks as an RMSF vector in eastern Arizona. It is important to continue monitoring RMSF infection to inform public health interventions that target RMSF reduction in high-risk populations.

To examine trends of Rocky Mountain spotted fever (RMSF) incidence among American Indians compared with other race groups, a retrospective analysis of national RMSF surveillance data reported to the National Electronic Telecommunications System for Surveillance and the Tickborne Rickettsial Disease Case Report Forms system were used. The RMSF incidence for American Indians, which was comparable to those for other race groups during 1990-2000, increased at a disproportionate rate during 2001-2005. The average annual incidence of RMSF reported among American Indians for 2001-2005 was 16.8 per 1,000,000 persons compared with 4.2, 2.6, and 0.5 for white, black, and Asian/Pacific Islander persons, respectively. Most cases in American Indians were reported from Oklahoma (113.1 cases per 1,000,000), North Carolina (60.0), and Arizona (17.2). The incidence of RMSF increased dramatically among American Indians disproportionately to trends for other race groups. Education about tick-borne disease and prevention measures should be addressed for high-risk American Indian populations.

To describe the epidemiology of ulcers, gastric cancer, and Helicobacter pylori infection among American Indian (AI) and Alaska Native (AN) persons, we analyzed hospitalization discharge records with physician discharge diagnoses coded as ulcer, gastric cancer, and mucosa-associated lymphoid tissue (MALT) lymphoma during 1980 to 2005, and H. pylori during 1996 to 2005 from the Indian Health Service Inpatient Dataset. The average annual age-adjusted rate of hospitalizations that included an ulcer-associated condition was 232.4 per 100,000 AI/AN persons. The age-adjusted rate for gastric cancer was 14.2 per 100,000 persons. MALT lymphoma was listed as a discharge diagnosis at an age-adjusted rate of 6.1 per 100,000, and the age-adjusted rate of H. pylori discharge diagnoses was 28.2 per 100,000. The AI/AN persons living in the Alaska region and thoseor= 65 years old had the highest rates of hospitalizations that listed ulcer-associated conditions, gastric cancers, MALT lymphoma, and H. pylori as a discharge diagnosis.

To describe the epidemiology of Rocky Mountain spotted fever (RMSF) among American Indians/Alaska Natives (AI/ANs), we conducted a retrospective analysis of hospitalization records with an RMSF diagnosis using Indian Health Service (IHS) hospital discharge data for calendar years 1980-2003. A total of 261 RMSF hospitalizations were reported among AIs, for an average annual hospitalization rate of 1.21 per 100,000 persons; two deaths were reported (0.8%). Most hospitalizations (88.5%) occurred in the Southern Plains region, where the rate was 4.23 per 100,000 persons. Children 1-4 years of age had the highest age-specific hospitalization rate of 2.50 per 100,000 persons. The overall annual RMSF hospitalization rate declined during the study period. Understanding the epidemiology of RMSF among AI/ANs and educating IHS/tribal physicians on the diagnosis of tick-borne diseases remain important for the prompt treatment of RMSF and the reduction of the disease occurrence among AI/ANs, particularly in high-risk areas.