The changing pattern of enteric protozoan infections in the Los Angeles area between 1996 and 2013

This is the first study of seasonal prevalence of parasitic infections over a period of 18 years in an urban/suburban setting anywhere in the world. We examined parasitological test results of 7766 fecal specimens from 3883 patients in the Los Angeles County, from 1996 to 2013 tested at Parasitology Center, Inc. (PCI), Scottsdale, Arizona. During this period, 1629 (41%) of patients were found infected with one or more protozoan parasites. The most prevalent parasites were Blastocystis hominis (19%), Entamoeba histolytica / E. dispar (6%), E. hartmanni (6%), and Cryptosporidium parvum (5%). Blastocystis hominis made up 45% of all infections. The prevalence of infections with Blastocystis hominis showed progressive decline through 2013. The reverse pattern was observed in infections with C. parvum. Infections with B. hominis were more prevalent in the cold months and lowest in August and September. Infections with C. parvum were most prevalent from March to June and lowest in August. The overall monthly prevalence rates for all protozoan parasites varied between 34% in August and 51% in February. An interpretation of the above findings is provided. Notable similarities and differences from other studies are noted, especially regarding the composition of the parasitic fauna diagnosed, annual prevalence rates, and seasonality.