—from Epidemiological
Bulletin , Vol. 25 No. 2, June 2004—
Case Definitions: Schistosomiasis
Rationale for surveillance
Schistosomiasis is the second most prevalent tropical disease (following
malaria) and a leading cause of severe morbidity in large parts of Africa, Asia
and South America. 600 million are at risk; 200 million are infected, of whom
20 million are severely ill.
The main goal for WHO is to control the disease, to reduce and even (in some countries) eliminate the risk of schistosomiasis through strong surveillance and control programs.
There are 2 types of clinical disease: urinary schistosomiasis (S. haematobium)
and intestinal schistosomiasis (S. mansoni, S. japonicum,
S. intercalatum, S. mekongi).
Recommended case definition: Intestinal schistosomiasis
Endemic
areas
Suspected: A person with hepatosplenomegaly.
Probable: Not applicable.
Confirmed: A person with eggs of S. mansoni or S.
japonicum in stools (microscope).
Non-endemic areas and low-prevalence zones
Suspected: Not applicable.
Probable: Not applicable.
Confirmed: A person with eggs of S. mansoni or S.
japonicum in stools (microscope).
Recommended case definition: Urinary schistosomiasis (this type is not present in the Americas)
Endemic areas
Suspected: Not applicable.
Probable: Not applicable.
Confirmed: A person with visible haematuria or with positive reagent strip
for haematuria or with eggs of S. haematobium in urine (microscope).
Non-endemic areas and low-prevalence zones
Suspected: A person with visible haematuria or with positive reagent strip
for haematuria.
Probable: Not applicable.
Confirmed: A person with eggs of S. haematobium in urine (microscope).
Recommended types of surveillance
Surveillance of schistosomiasis must be incorporated into the primary health
care system.
For low-prevalence zones, and where elimination is targeted
Routine monthly reporting of aggregated suspected or confirmed cases from peripheral
level to intermediate and central level.
International. Yearly reporting from central level to WHO.
For endemic zones
If no integration of surveillance is possible in the primary health care system:
ad hoc surveys to evaluate the prevalence of infection in the community.
Children of school age have been identified as a good indicator of prevalence
in the general population and therefore an appropriate group for investigation.
Yearly reporting of aggregated data from peripheral level to intermediate and
central levels.
Note
• Data from general health statistics often underestimate prevalence but
may nevertheless indicate a relatively high prevalence in a particular area.
• Surveillance has to take into account the distribution of the disease
in geographical foci. Adjacent areas may have very different prevalence rates.
Recommended minimum data elements
For low-prevalence zones, and where elimination is targeted
Individual patient record for investigation:
Identification number, age, place of infection, date of diagnosis, village.
Number of eggs per gram of stools or ml of urine.
Aggregated data:
Number of cases by age group and village and month.
Number of cases with >1 egg/10 ml of urine and / or visual haematuria (S.
haematobium).
Number of cases with >1 egg/g of stools (S. mansoni or S. japonicum).
For endemic zones
Aggregated data:
Number of cases by age group and village.
Number of cases with >1 egg/10 ml of urine and/or visual haematuria (S.
haematobium).
Number of cases with >1 egg/g of stools (S. mansoni or S.
japonicum).
Recommended data analyses, presentation, and reports
• Incidence (if passive reporting or passive surveillance) monthly and yearly
by age group and village
• Point prevalence (if active finding)
• Mapping
For school-age children 1
• Prevalence of infections (percentage of infected individuals) in a population
• Proportion of heavily infected individuals
Principal uses of data for decision-making
• Assess the magnitude of the problem
• Plan drug distribution: select cost effective strategy for chemotherapy
(universal-targeted-selective)
• Evaluate the need for snail control
• Evaluate the need for improved water supply and sanitation
• Evaluate the need for health education activities
• Evaluate the impact of intervention
Special aspects
• Diagnosis: quantitative diagnostic methods (Kato-Katz technique
for intestinal forms, urine filtration for S. haematobium) are very important
in surveillance; they indicate the public health relevance of the infection.
• Collection of data immediately relevant to management decision (e.g.,
treatment frequency and resource allocation) should be encouraged.
• Intersectoral efforts, emphasising school education, safe water supply
and sanitation, environmental management and community participation are important.
• Rectal biopsy is usually not used for surveillance purpose.
Return to index
Epidemiological
Bulletin , Vol. 25 No. 2, June 2004