# P-1773. Intestinal Parasitic Infections in Japan: Cross-sectional Study of Prevalence and Risk Factors in Suspected Infectious Gastroenteritis

## TL;DR

This study examines the prevalence and risk factors of intestinal parasitic infections in Japan, finding that certain parasites are increasingly linked to sexual transmission and zoonotic spread.

## Contribution

The study identifies new risk factors for intestinal parasitic infections, including sexual transmission among men who have sex with men and zoonotic transmission.

## Key findings

- Intestinal parasitic infections were confirmed in 9.9% of 624 examined stool samples.
- Domestic infections were limited to Giardia duodenalis, Entamoeba histolytica, and Cryptosporidium spp., while imported cases showed a wider variety of parasites.
- Risk factors included recent travel to endemic areas, being a man who has sex with men, and animal contact.

## Abstract

In developed countries, intestinal parasites are generally considered as an agent occurring among people who are traveling to or immigrants from endemic area with poor sanitation. Also, recent epidemiological studies showed that Entamoeba histolytica could happen as sexually transmitted infection (STI). However, the epidemiology of the other intestinal parasite infestations (IPIs) is still unclear in many developed countries.Figure 1.Distribution of intestinal parasites.Intestinal parasitic infections were determined by modified O&P in the present study. (A) Intestinal parasites seen in imported cases were presented, in which multiple parasites were detected from one sample in two cases. (B) Intestinal parasites seen in domestic cases are presented, in which multiple parasites are detected from one sample in four cases.Table 1.Impact of patients’ characteristics and symptoms on the incidence of IPIs.*Multivariate analysis was calculated for an independent variables, which were adjusted by sex, age, and variables with relatively low p value (p < 0.2).

Distribution of intestinal parasites.

Intestinal parasitic infections were determined by modified O&P in the present study. (A) Intestinal parasites seen in imported cases were presented, in which multiple parasites were detected from one sample in two cases. (B) Intestinal parasites seen in domestic cases are presented, in which multiple parasites are detected from one sample in four cases.

Impact of patients’ characteristics and symptoms on the incidence of IPIs.

*Multivariate analysis was calculated for an independent variables, which were adjusted by sex, age, and variables with relatively low p value (p < 0.2).

For stool samples from the patients with suspicion of infectious gastroenteritis, modified stool ova and parasite examination (modified O&P) was performed as following. Firstly, stool samples are mixed with fluorescent conjugated antibodies against Giardia cyst, and Cryptosporidium oocyst, thereafter, the sample is examined by both fluorescent microscopy and bright-field microscopy. It has compatibly high sensitivity as antigen detection test or PCR for the detection of these protozoa.

During 3-year study period, 624 stool samples were examined by modified O&P. IPIs were confirmed in 62 cases (9.9%); 30 as imported cases and 32 as domestic cases (Fig. 1). The most common parasites were G. duodenalis, E. histolytica, and Cryptosporidium spp. Interestingly, domestic parasite infections were limited to these three protozoa, in which four cases showed multiple protozoa.

In contrast, various types of parasites were detected in imported cases. Multivariate logistic regression identified not only recent travel history to endemic area but also men who have sex with men and animal contact as independent risk factors for IPIs (Table 1).

G. duodenalis and Cryptosporidium spp. are commonly reported as domestic cases, whose frequency was the same level as that of E. histolytica. Also, the results from regression analysis suggest that these protozoa are spreading as sexually transmitted infection among MSM, and zoonoses. Molecular epidemiological study is currently underway. Active epidemiological surveillance is warranted in the other developed countries.

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