Deaths from infections have fallenin general over the past century, except for the spike during the Spanish flu epidemic of 1918, and leveled off after 1950. But the introduction of new viruses into the population at various time points has brought an evolution in the types of infections affecting the population.
"This (study) gives us really good information about the impact diseases are having" on mortality, said Heidi Brown, associate professor of public health at the University of Arizona, who led the research. "Diseases change ... and we have the capacity for the introduction of new pathogens (bugs)."
Finding a general decline since 1900, the study, published Tuesday, focused on infections causing greater numbers of deaths in more recent years.
By analyzing trends in USmortality between 1980 and 2014, scientists found that infections were responsible for 5.4% of all deaths, with the majority caused by influenza and pneumonia.
The number of deaths due to infection rose between 1980 and 1995 after the arrival of HIV, but numbers declined steadily from 1996 with the introduction of antiretroviral therapy, highlighting the impact made by the new treatment.
"Look at what we can do when we come together and challenge a disease like HIV," Brown said.
The proportions of people dying from influenza and pneumonia, however, have not changed too much over this time frame, with approximately 17 out of 100,000 people dying from one of the two diseases.
Brown highlighted that "a lot of diseases end with pneumonia," the infection and inflammation of the lungs caused by a range of organisms, including bacteria, viruses and parasites. Influenza and pneumonia "are something we have been dealing with for a long time and are still dealing with," she said.
Vector-borne diseases have also risen since 1980, with the arrival of more diseases spread via insects, including West Nile virus. Though deaths from West Nile virus -- which is symptomless in 80% of those infected but can result in a fatal neurological disease -- are low at just 0.03 per 100,000 in 2014, the increase from zero shows the potential for new diseases to establish themselves.
"West Nile is not a huge killer in the US," Brown said. "But it's a reminder we are still at risk of the introduction of new diseases."
Diseases that can be prevented through vaccination, such as measles and polio, have seen a decline since 1980, and deaths from drug-resistant infections have remained fairly stable. But Brown flagged that certain bacteria, such as hospital-acquired clostridium difficile, have risen since 1980, with a steeper rise after 2000.
"These are one of our vulnerabilities," she said, adding the importance of distinguishing which infections are affecting the population at different times. "We tend to lump infectious diseases (together), and this helps us break that down a bit."
The team stresses that although this study show trends over time, it is just part of the picture. It focuses only on people dying from infectious diseases, not the numbers that become infected and suffer symptoms. However, "it's a reminder of what infectious disease look like and where are risks are."
Commenting on the findings, Dr. Rosalind Eggo, research fellow at the London School of Hygiene & Tropical Medicine, said, "the decrease in infectious disease burden in the US is a result of improved living conditions, better sanitation and modern medical care. In the later period of the study. Eggo, who models the transmission and patterns of infectious diseases, was not involved in the study.
"The huge benefit of vaccines is clear, with large decreases in mortality from vaccine preventable diseases," she said.
But Eggo added the importance of being aware of all potential areas of vulnerability. "There is uncertainty in the impact of vector-borne diseases in the US. ... The effect of changing climate may alter which geographic areas are at risk from vector-transmitted infections.
"Drug resistance is a growing problem and requires urgent action to tackle it. Antibiotics are a key weapon in the battle against bacterial infections, but we must use those tools carefully to make sure they stay effective."