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Mortality rates from infectious diseases in the U.S. declined almost 19% in the last 35 years, although large differences were observed across counties, researchers found.

There were 41.95 deaths per 100,000 due to infectious diseases in 1980 compared with 34.10 deaths per 100,000 in 2014, for an overall decrease of 18.73%, reported Charbel el Bcheraoui, PhD, of the University of Washington in Seattle, and colleagues.

Lower respiratory infections were the most common cause of infectious disease mortality in 2014, accounting for nearly 80% of total deaths from infectious disease, the authors wrote in the

Using "innovative" techniques, they estimated age-standardized mortality rates, as well as trends by county for several types of infectious diseases that caused 1% or more of deaths due to infectious diseases from 1980 to 2014, including lower respiratory infections, diarrheal diseases, HIV/AIDS, meningitis, hepatitis, and tuberculosis.

In addition to prior research from the reporting declines in infectious disease mortality at state and national levels, they argued that local data "is particularly relevant to local public health leaders in making decisions around resource allocation and focusing of treatment efforts." They added that national and state-level estimates can sometimes be misleading because they can "mask variations at the local level."

The authors utilized a combination of deidentified death records from the and population counts from several sources, including the , NCHS, and the

Overall, there were 4,081,546 deaths from infectious diseases in the U.S., comprised of the six above categories, several infectious diseases that caused a small number of deaths and deaths attributed to "other infectious diseases." There were a total of 113,650 deaths in 2014 versus 72,220 deaths in 1980.

Lower respiratory infections were the most common cause of infectious disease mortality in 2014, with a rate of 26.87 (95% uncertainty interval 25.79-28.05) deaths per 100,000 persons, which accounted for 78.80% of all infectious disease deaths.

An by Emily K. Shuman, MD, and Preeti N. Malani, MD, both of the University of Michigan in Ann Arbor, noted that lower respiratory infection had the greatest variation in mortality among U.S. counties, and speculated that certain demographic factors may play a role.

"Persons with low income, homelessness, incarceration, and African American race/ethnicity have an increased risk of bacteremic pneumonia," they wrote. "A recent study of Tennessee Medicaid recipients also suggested that prescription opioid use ... was associated with increased risk of invasive pneumococcal disease."

Diarrheal diseases were the second leading cause of mortality, at a rate of 2.45 deaths per 100,000 persons (7.07% of infectious disease deaths), and Bcheraoui's group noted they were the only cause of infectious disease mortality to rise from 2000 to 2014. Indeed, mortality rates from diarrheal disease increased in nearly all counties.

Shuman and Malani said that this increase was likely due to the emergence of epidemic Clostridium difficile infection, and cited statistics from indicating that C. difficile infection is "currently the leading cause of gastroenteritis-associated deaths in the United States" (48.3% of those deaths).

HIV/AIDS was third leading cause of mortality from infectious diseases, comprising 7.04% of all deaths, for a rate of 2.40 per 100,000 persons. Bcheraoui's group said that HIV/AIDS had the highest relative mortality inequality between counties, and cited these "notable geographic patterns."

"HIV/AIDS mortality increased first in some of the wealthiest US counties on the West Coast, but has shifted to some of the poorest counties in the southeastern United States," they wrote. "Overall, the trend of HIV/AIDS mortality reflected the availability of and advancement in treatment."

Study limitations included that fact that all deaths, population, and covariates data are subject to error and "the garbage code redistribution methods" used in the study "have not been validated due to insufficient criterion standard (autopsy) data," the authors explained.