Helminthiases are widely spread around the world, especially in tropical areas, where local people have poor hygiene and lower income economies, such as Africa and Asia, including Vietnam. For example, human fascioliasis has been reported in more than 70 countries in Europe, the Middle East, Latin America, the Caribbeans, Africa, Asia, and Oceania [1]. Clonorchiasis is distributed in many countries such as South Korea, China, Taiwan, Vietnam, Japan, and Russia with 35 million infected cases in the world, including 15 million in China [2]. Toxocariasis is widespread, including the Americas, Japan, Canada, Germany, England, Italy, France, and Russia; in some areas the infection rate is up to 35–42% [3]. Based on serological examinations, the prevalence of toxocariasis has been reported to be 30–93% in developing countries [3]. Angiostrongyliasis due to Angiostrongylus cantonensis is distributed in more than 30 countries in Asia, Africa, the Caribbeans, Australia, and USA (Hawaii and Louisiana) with over 2,800 cases [4]. Strongyloidiasis caused by Strongyloides stercoralis is also widespread in the world with 30–100 million cases and are the cause of diseases of the intestine, lungs, skin, and others [5]. Gnathostomiasis has been detected in many countries, including Japan, Thailand, Cambodia, Laos, Myanmar, Indonesia, the Philippines, Malaysia, Vietnam, China, India, and Sri Lanka [6,7]. Cysticercosis due to infection with the metacestode of Taenia solium is distributed in wide areas of Asia, Africa, the Americas, and Oceania. In some areas, the prevalence of cysticercosis was 10% where neurocysticercosis was the cause of severe cerebral diseases [8].

In Vietnam, helminthic diseases are distributed all over the country, including fascioliasis in 63 of 63 provinces, clonorchiasis/opisthorchiasis in 32 of 63 provinces, and cysticercosis in 50 of 63 provinces; toxocariasis, strongyloidiasis, angiostrongyliasis, and gnathostomiasis are detected in every province of the country [9–12]. However, there have been no recent data to estimate the present status of these helminthic infections among hospital patients around Hanoi region. Therefore, the present study was performed to estimate the prevalence of tissue and luminal helminthiases, including toxocariasis, strongyloidiasis, gnathostomiasis, cysticercosis, fascioliasis, angiostrongyliasis, and clonorchiasis, using ELISA among the patients who visited Hanoi Medical University Hospital during 2018 (from 27 of 28 northern provinces), Hanoi, Vietnam.

The most common reasons (clinical complaints) for the patients who came to the hospital included headache (26.6%) and stomachache (23.7%). Of the 1,120 patients who were from 27 of 28 northern provinces in Vietnam and came to Hanoi University Hospital for examination, 64.0% (717 patients) showed seropositive results for tissue or luminal helminthiasis. The number of patients from Hanoi City was the highest (112 patients) but the helminthic infection rate was the lowest (59.8%); the highest infection rate was observed from Lai Chau Province (75.0%).

Toxocara spp. infection rate was 59.0%, which was the highest in this study compared to previous reports [11–15]. In the laboratory of hospitals and medical centers, Toxocara infection was 45.2% [12] and 65.1% [13] before this report. In the community, Toxocara infection was 24.4% in southern provinces [14] and 17% in middle provinces [15]. The seroprevalencse of toxocariasis was reported from other countries; in Nigeria 30%, Brazil 36%, Swaziland 44.6%, Malaysia 58%, Indonesia 63.2%, Nepal 81%, Marshall Islands 86.8%, and La Reunion 93% [3,16]. The prevalence of Toxocara in rural areas was higher than that in urban areas (35–42% and 2–5%, respectively) [3]. The remarkably high seroprevalence of toxocariasis in northern Vietnam is probably due to high soil contamination with canine (Toxocara canis) or feline (Toxocara cati) feces containing the infective eggs.

The seroprevalence of S. stercoralis infection in this study was 46.3%. In other studies from Hanoi Hospital, the prevalence was was 20.0% [17], and in Ho Chi Minh Hospital 29.0% among the stomachache patients group [11]. In the laboratories, the prevalence was 22.5% [13] and 7.4% [12], and in the community 7.6% [18] and 17.3% [14]. S. stercoralis prevalence in other countries was 17.5% in Cambodia, 26.2% in Laos, and 23.7% in Thailand [19].

The seroprevalence of Gnathostoma spp. (mostly presumed to be G. spinigerum) infection in our study was 25.5%. In the Ho Chi Minh Hospital, Gnathostoma infection was 15.6% [13], but in the community, the prevalence was 6.8% in the middle of the country [20] and 17.3% in the south of the country [14]. The prevalence of cysticercosis in this study was 12.8%. In Ho Chi Minh Hospital, the prevalence was 9.8% [13] and 4.9% [12]. In the laboratory of Hanoi Hospital, the prevalence was 15.8% [9], and in the community, the infection rate in the north was 7.2%, and that in the south was 4.3% [9] and 5.1% [14].

Fasciola spp. infection was positive in 11.2% among 1,120 examined patients. In the laboratory of Ho Chi Minh Hospital, its prevalence was 11.2% [13] and 5.9% [12]. In the community, Fasciola infection rate was 11.0% [21] and 7.8% [22] in the middle of the country, and that in the north was 19.3% [14]. A. cantonensis infection was positive in 10.5%. In another study using PCR technique demonstrated that A. cantonensis was responsible for 67.3% of 55 cases of eosinophilic meningitis from a cohort of 1,690 adult patients at a tertiary hospital in southern Vietnam [23]. The prevalence of C. sinensis infection was 8.7%. In the community, where local people used to eat raw fish, the prevalence was up to 40.0% [9]. C. sinensis infection rate was higher in males than in females.

Most of the patients in this study had multiple infections (53.0%) and mono-infection was lower (11.1%); most of the patients were infected with 2–3 helminth species. The highest prevalence was seen in the age group of 51–70 (76.0%), and the lowest was in the age group of 5–10 (34.0%). In another study in Ho Chi Minh Hospital, the proportion of multiple helminthiases was 45.7–54.3% [12]. In the community, it was shown that Toxocara infection in the age group of >15 years was higher than that in the age group of ≤15 years (19.9% and 12.8%, respectively) [15]. The number of patients was the highest in May, June, and July, and this was similar with the results of De et al. [10] for a fascioliasis study in 2020 [10].

In conclusion, the overall seroprevalence of helminthic infections in the Parasitology Laboratory of Hanoi Medical University Hospital in 2018 was 64.0%, which included toxocariasis (59.0%), strongyloidiasis (46.3%), gnathostomiasis (25.5%), cysticercosis (12.8%), fascioliasis (11.2%), angiostrongyliasis (10.5%), and clonorchiasis (8.7%). Most of the patients had multiple infections with 2–3 species of helminths. Eosinophilia was observed in 80.2% of the total seropositive patients.