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APPENDIX I. CASE DEFINITIONS AND SURVEILLANCE SYSTEMS FOR ARBOVIRAL ENCEPHALITIS
National surveillance data for human arbovirus encephalitis is collected on a monthly basis during the transmission season from April through October of each year. State and Territorial epidemiologists are encouraged to report all Probable and Confirmed cases (see "Case definitions for arboviral encephalitis") using the Human Arboviral Encephalitis Surveillance Form (CDC 55.3, Figure I-1). The data are periodically summarized and reported back to State and local agencies through informal bulletins and through an annual summary of disease activity published in the MMWR. State and local public health agencies are also encouraged to immediately report outbreaks and unusual occurrences of arbovirus encephalitis directly to the Division of Vector-Borne Infectious Diseases (DVBID), NCID, CDC.
Data on arbovirus activity in wild birds and mammals, as well as in insect vectors, also are reported to the DVBID surveillance program, using CDC Forms 3.940A/B (Figure I-2). When reporting data for vectors or wild vertebrate hosts, it is helpful to have the data pooled by county (or city, if a local program). When reporting cases in equines or other domestic animals, it is very helpful to have the state case or specimen accession number. This number helps to prevent "double counting" of cases that may be reported via several systems.
Case definitions for arboviral encephalitis 52
The following definitions are presented to assist in defining the level of certainty attached to reports of encephalitis in humans.
Possible cases of arboviral encephalitis include persons with:
Probable cases include persons that meet this clinical definition AND:
Confirmed cases of arboviral encephalitis include persons that meet this clinical definition AND:
Existing Surveillance Programs at the State and Local Level
In 1991, state health and vector control agencies were surveyed by DVBID and the State Public Health Vector Control Conference (SPHVCC) to determine the extent and form of arboviral surveillance at the state and local level. In addition, selected large local vector control programs were included in the survey. The responses to the questionnaire are summarized in Table I-1.
It is clear that arbovirus surveillance programs vary widely in format and level of specialization. In general, large, highly developed programs tend to be located in areas with a history of arboviral encephalitis activity. However, it is probably also true that relatively more cases of arboviral encephalitis go undetected in areas that lack the capability for routine monitoring and detection of virus activity in vectors, wild vertebrate hosts, humans or domestic animals.
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