Air pollution, even of short duration, increases the number of lower respiratory infections, a study reports, and the effects may be particularly serious in young children.

Acute respiratory infection of the lungs and airways, usually caused by viruses, are a leading cause of illness and death in young children.

The study, in the American Journal of Respiratory and Critical Care Medicine, tracked 146,397 people, 77 percent of them younger than 2, who had infections treated in hospitals and clinics in Utah. Researchers gathered data on levels of small particulate matter, or PM2.5.

They calculated that each short-term increase of 10 micrograms per cubic meter in PM2.5 is associated with a 15 to 23 percent increase in serious respiratory infections.

Brain injuries tied to dementia risk

In the largest study of its kind, researchers have found that traumatic brain injury is associated with an increased risk of dementia. The risk of dementia was highest among people who had suffered multiple TBIs. But even a single mild TBI was tied to an increased risk of dementia.

The study, in Lancet Psychiatry, used Danish health databases that included all residents as of Jan. 1, 1995, who were at least age 50 at some time during the 36-year follow-up, from 1977 to 2013. Among 2,794,852 people, they found 132,093 who had had at least one TBI.

They found that compared with people who had never had a TBI, those who had had any were at a 24 percent increased risk for dementia, and those who had had five or more had nearly triple the risk. Even a single mild TBI increased the risk by 17 percent.

Officials track source of listeria outbreak

The world’s largest known listeria outbreak has spread throughout South Africa for 15 months, killing 189 people. Health officials believe they have identified the source: bologna.

Since January last year, 982 confirmed cases of listeriosis had been recorded, the National Institute for Communicable Diseases in South Africa reported. The infection, caused by food that has been contaminated with the bacterium Listeria monocytogenes, is often lethal.

A cluster of gastroenteritis cases among toddlers in a Johannesburg hospital this January led authorities to the sandwich meat in a day care center’s refrigerator — and in turn, to a meat production facility in Polokwane. There, officials said they detected traces of LST6, the listeria strain identified in 91 percent of the cases.

Listeriosis has an incubation period of up to 70 days, so additional cases are expected to emerge.

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