American trypanosomiasis (Chagas' disease)
Rationale for surveillance
Targeted by WHO for elimination by the year 2010 (Resolution WHA51.14), American trypanosomiasis affects 21 countries with 16-18 million infected and over 100 million individuals at risk of infection.
The disease is prevalent in the northern part of South America (the Andean Region) and in Central America; almost 25 million people are at risk and there are 5 to 6 million infected.
It is a chronic, potentially fatal disease. One third of those infected become incapacitated due to cardiac damage or digestive megaformations.
Infection can also be acquired through blood transfusion and congenitally through the placenta.
The infection can be effectively eliminated through interruption of vector transmission and systematic screening of blood donors, with selection of donors and disposal of infected blood. Elimination has been very successful in some countries of the Southern Cone of South America (Argentina, Brazil, Chile and Uruguay).
Surveillance is necessary for prevention and control measures.
Recommended case definition
The main clinical signs are mainly fever, malaise, hepatosplenomegaly and lymphadenopathy in the acute phase. Many patients present without clinical signs. An inflammatory response at the site of infection (chagoma) may last up to 8 weeks.
Laboratory criteria for diagnosis
Positive parasitology (direct, xenodiagnosis, blood culture) and/or
Positive serology for Trypanosoma cruzi antibodies in two patterned reactions (indirect haemagglutination test (IHA), indirect immunofluorescent antibody test (IFAT)
Suspected: Not applicable.
Probable: Acute case in endemic areas: person with unexplained fever, hepatosplenomegaly and a chagoma (inflammation at site of infection).
Confirmed: A clinically compatible case that is laboratory-confirmed with positive parasitology or serology with two positive patterned reactions.
Indeterminate: Positive serology for T. cruzi antibodies in two reactions.
Congenital: Newborn with hepatosplenomegaly with positive xenodiagnosis in zones where the disease is endemic, or an asymptomatic child of a seropositive mother with positive parasitology or serology that is persistently positive over a three-month period.
Blood donor: screening positive serology for T. cruzi, confirmed by two patterned tests.
Recommended types of surveillance
In endemic areas, sentinel surveillance and periodic surveys in populations at risk are the feasible methods at present.
Where possible, routine surveillance should be integrated in primary health services. At peripheral level, individual patient records must be maintained.
Routine monthly reporting of aggregated data for acute cases from peripheral level to intermediate level. Routine biannual reporting of aggregated data to central level.
All blood donations must be screened locally.
Serological surveys (standardized and periodical) for surveillance and control.
Recommended minimum data elements
Individual patient records
Unique identifier, name, age, sex, geographical and environmental information, laboratory results.
Aggregated data for reporting:
Number of cases identified from transfusion donors
Number of cases by age / sex / means of diagnosis
Number of cases with positive serology
Number of houses and localities infested by triatoma
Number of houses and localities subject to annual vector control
Isolate-based data for reporting*
Scientific name of organism, clinical form, organ or tissue, geographical information (patient location), date of isolation, name of laboratory, laboratory number of isolate, identification methods used, results.
Recommended data analyses, presentation, reports
Graphs: Number of cases by geographical area, month, and means of diagnosis.
Maps: Number of cases by geographical area
Vector control activities / geographical area / prevalence of disease.
Principal uses of data for decision-making
Monitor disease prevalence and measure the impact of disease
Monitor control and elimination program
Target resources for prevention
Control has depended on vertical programs. Monitoring and surveillance have been conducted through specific surveys. The current control trend is to integrate the control program into primary health care, which requires a network of laboratory services with different facilities with differentiated levels of complexity at different levels for diagnosis.
Because of variation in specificity of the tests, cut-off points for reliability should be defined locally using a standard serum panel, provided by the reference laboratories of the intercontinental network for standardized serology in Brazil and Argentina.
A national laboratory network should be established in each of the countries in which Chagas disease is endemic.
* (WHO technical Reports Series N° 811: Control of Chagas disease. Geneva: World Health Organization, 1991: 77-78)
Source: WHO Recommended Surveillance Standards, Second Edition, October 1999, WHO/CDS/CSR/ISR/99.2
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Epidemiological Bulletin, Vol. 24 No. 3, September 2003