Naegleria fowleri Infection (cont.)
What are risk factors for Naegleria fowleri infection?
The source of nearly all of the 128 Naegleria fowleri infections reported since 1962 in the U.S. has been exposure to warm freshwater. These include freshwater lakes and rivers, particularly in Texas and Florida. More than one-quarter of all cases are reported from Florida and most cases have occurred in the South, although recent cases have been reported from Minnesota, from Lake Havasu City in Arizona, from Los Angeles in California, and other sites. Other freshwater sources have included hot springs, poorly chlorinated pools, untreated well water, water heaters, neti pots, and warm water discharge from power plants. Of the 31 cases reported from 2003 to 2012, 28 people acquired the disease from recreational exposure to freshwater and three people acquired it from irrigating their nose with contaminated tap water. There is a decided summertime predominance of cases, and even lakes in the southern States have higher levels of this microbe commonly during the warmer months.
More than 75% of cases since 1962 were in children or adolescents, and 75% or more were in males. It is known that exposure of the olfactory nerve to contaminated water is the portal of entry to the brain. This exposure often results from water being forcefully introduced into the nose during trauma such as dunking, diving, or crashing while water skiing.
Hundreds of millions of people go to swimming venues where N. fowleri is found, but fortunately very few become infected. We are unable to calculate an accurate estimate of the true risk of invasive Naegleria fowleri infection.