The incubation period of cryptosporidiosis is usually 4-8 days and symptoms such as nonhemorrhagic watery diarrhea last for about 10 days (range 2-26 days). Excretion of oocysts may continue even after the disappearance of symptoms for as long as approximately 2 months (see p. 170 of this issue). When immunosuppressed patients are affected, the disease tends to be prolonged and severe. Treatment of HIV/AIDS patients with paromomycin or nitazoxanide are currently being attempted (see http://www.ims.u-tokyo.ac.jp/didai/orphan/index.html, the Research Group on Chemotherapy of Tropical Diseases, Japan Health Science Foundation). Improving the immune function of these immnosuppressed cases has resulted in an increase in positive therapeutic outcomes (see p. 174 of this issue). In August 1997, the MHW called attention to the prevention of Cryptosporidium infection among immunosuppressed persons such as AIDS patients.
Etiological diagnosis: About 13 species of protozoa in the genus Cryptosporidium have been reported from various living species, such as mammals, reptiles and fishes. Human infection occurs mostly with C. parvum . In laboratory diagnosis, oocysts are detected by microscopic observation (see http://www.nih.go.jp/niid/para/atlas/japanese/manual/cryptosporidium.pdf). The fluorescent-antibody staining method (insurance inapplicable as a laboratory reagent) highly sensitive in detecting oocytes, and is widely used in examinations of tap water. Molecular epidemiological methods are progressively being used to investigate sources and routes of infection (see p. 174 of this issue).
National Epidemiological Surveillance of Infectious Diseases (NESID): Cryptosporidiosis, in addition to other enteric protozoal infections such as giardiasis and amebic dysentery, are considered category V notifiable infectious diseases in the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law), requiring all physicians to report any identified cases. During April 1999 to June 24, 2005, the period of enactment of the Infectious Diseases Control Law, 233 cases were reported (Table 1), a large increase from the last Topic of This Month (IASR 22:159-160, 2001). However, cases were reported from 10 prefectures in the Hokkaido, Kanto, and Kansai districts (Fig. 1). Most cases were part of outbreaks occurring in 2002 (100 cases) and 2004 (80 cases), while in those other than these cases, reported were 53, being 3-13 cases annually (Fig. 2). Reported cases of cryptosporidiosis, including cases from outbreaks, have been considerably fewer than those of giardiasis (614 cases) and amebic dysentery (2,998 cases).
The age range of 53 non-outbreak related cases was 17-88 years, with a peak occurrence among those 20-24 years; a 5:1 male to female ratio was observed (Fig. 3). These observations may be explained by the fact that cryptosporidiosis is often seen as an opportunistic infection in HIV/AIDS patients. In contrast, the sex ratio during an outbreak in Ogose Town, Saitama Prefecture, was approximately 1:1.
Of the 53 non-outbreak related cases, 32 were infected domestically while 21 acquired infection abroad. Among the domestic infections, contact with livestock and homosexual contact were mentioned in many reports (Table 2). Suspected small outbreaks of disease among male homosexuals in Tokyo and its vicinities have been reported (see p. 174 of this issue). Most of the 14 cases were presumably infected while traveling in the Indian subcontinent, although three were infected in Africa, two in China, and one each in Vietnam and South America.
Outbreaks: Cryptosporidium has often caused large-scale waterborne infections. In 1993, 400,000 people were infected by a water-supply accident in Milwaukee, Wisconsin, US. In Japan, large outbreaks also occurred in Hiratsuka City, Kanagawa Prefecture in 1994 (see IASR 15:248-249, 1994) and Ogose Town, Saitama Prefecture in 1996 (see IASR 17:217-218, 1996). Waterborne cryptosporidiosis is characterized by very high morbidity; in Milwaukee, as high as 52% and in Ogose Town 70% (8,700 people) of all city-water recipients were affected.
After the last Topics of This Month, four outbreaks have occurred in this country; three in 2002 and one in 2004. Two outbreaks occurred in February and April 2002 among groups traveling to the Iburi area, Hokkaido; one in students from a high school in Hyogo Prefecture (see IASR 23:145-145, 2002), two months later another one in students from a professional school in Sapporo City (see p. 171 of this issue). Neither the source of infection nor transmission routes was identified.
Outbreaks caused by contacts with animals: During an outbreak that occurred in June 2002, high school students from Chiba Prefecture developed disease after visiting a pasture in Tokachi area, Hokkaido, reporting a history of contact with calves (see p. 172 of this issue). In Scotland, an outbreak occurred in a petting zoo in late April of this year (see Eurosurveillance Weekly, Issue 17, 2005). Because there are many similar facilities in Japan, health surveillance and control of animals, in addition to adequate hygiene instructions to visitors, are needed at these facilities. In May 2003, the Ministry of Health, Labour and Welfare issued guidelines on the prevention of zoonotic disease at animal exhibition facilities to enhance awareness among the general public (refer to http://idsc.nih.go.jp/jinju_hp/guideline03/index.html).
Outbreaks through swimming pools: In August 2004, groups of primary school, high school and college students were infected through swimming pools and other facilities at a camping facility in Nagano Prefecture. Morbidity was greater than 90% among the primary school group that used the swimming pool (see p. 167-169 of this issue). Infected children from this outbreak subsequently contaminated a swimming pool in Chiba Prefecture, resulting in another outbreak of cryptosporidiosis (see. p. 169 of this issue). In the US, 62 waterborne outbreaks were reported during 1991-2002, of which 50 were caused by contaminated water in swimming pools and other facilities mMMWR, 42 (SS05),1993; 45 (SS01), 1996; 47 (SS05), 1998; 49 (SS04), 2000; 53 (SS08), 2004n.
With the arrival of summer, it will be necessary to maintain hygienic management of recreational water facilities, and to conduct surveillance and appropriate measures in response to outbreaks, including restricting the use of swimming pools by cases of cryptosporidiosis and other diarrheal diseases. For early detection of Cryptosporidium infection, protozoan laboratory testing of stool specimens from diarrheal patients should widely be performed (see p. 168 of this issue).