EPIDEMIOLOGY

How common is N. fowleri?

Infection with N. fowleri is relatively rare--since N. fowleri was first described in 1965, about 300 cases of primary amebic meningoencephalitis have been reported. It is most often seen in healthy, active, young people. This may be because this population is most likely to be exposed to the organism through swimming or diving in infected water.

Interestingly, although infection is rare, N. fowleri is very common. A survey of lakes in Florida showed that 46% have N. fowleri. In addition, antibodies to N. fowleri is widespread in the population, indicating that exposure is common.

Where is N. fowleri found?

N. fowleri is found in warm, moist environments like soil and fresh water. Although soil is the preferred environment, heavy rains and runoffs often introduce the organism to bodies of water, where most humans are exposed.

N. fowleri is most likely seen in warm, stagnant water like lakes, ponds, and thermally polluted streams. Under these conditions, the bacteria the organism feeds on is more abundant. The risk of N. fowleri increases as water temperature rises, and the organism is most likely to invade bodies of water during hot, dry weather in the summer. It can grow in waters as warm as 45 degrees Celcius.

N. fowleri has been found in a wide variety of water sources, including coastal water, freshwater, sewage, poorly chlorinated swimming pools, artificial lakes, hot tubs, and hot springs. In one case of PAM, the organism was even traced back to the household water supply.

Worldwide distribution

N. fowleri is distributed worldwide. Cases of primary amebic meningoencephalitis (PAM) have been reported on all continents except Antartica. The majority of cases have been seen in developed countries--75% of cases have been from the United States, Australia, and Czechkoslovia--but this is probably due to better reporting and greater awareness of disease.