To the Editor: We report three cases of locally acquired Entamoeba histolytica infection in men who have sex with men (MSM) in Sydney, New South Wales.

E. histolytica is an invasive pathogenic amoeba that can cause invasive intestinal and extraintestinal amoebiasis. Entamoeba dispar is morphologically identical but is considered non-pathogenic and non-invasive.1

The three patients presented with a 1–3-week history of diarrhoea and abdominal pain. Routine bacterial cultures were negative for pathogens. Ova, cyst and parasite investigations showed cysts and trophozoites of E. histolytica/dispar complex in permanently stained, fixed faecal smears. Stool samples were tested for E. histolytica and E. dispar by polymerase chain reaction (PCR), using a previously described method.2 All three patients were positive for E. histolytica by PCR; sequencing of the amplicons verified the presence of E. histolytica DNA.

The three patients presented within a 12-month period in 2005–2006. All were homosexually active men (ages, 31–53 years) who lived in inner Sydney. None had a history of overseas travel within the previous 5 years, suggesting that the infections were locally acquired.

High rates of intestinal parasitism are found in MSM throughout the world. Oral–anal and oral–genital sexual practices are reported to predispose to infection with enteric pathogens, particularly protozoa. A 1991 study reported a higher prevalence (37%) of E. histolytica/dispar complex in a homosexual population in Sydney when compared to non-MSM.3 However, that study did not differentiate between the two species E. histolytica and E. dispar.

Amoebiasis has become endemic in MSM in Japan and causes significant morbidity and mortality; complications such as colitis and liver abscesses occur more frequently in homosexual and bisexual men than in heterosexual men.4 Similar findings on amoebiasis are reported from Taiwan, with MSM at increased risk for invasive amoebiasis and intestinal colonisation with E. histolytica.5

The discovery of E. histolytica infection in MSM in Australia is of public health concern and highlights the importance of continued surveillance, as the organism has the potential to become endemic in the gay population and to cause significant morbidity. Clinicians should also be aware that E. histolytica is present in urban settings in Australia and should be included in differential diagnoses.