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ArboNET, the national arboviral surveillance system, was developed by CDC and state health departments in 2000 in response to the emergence of WNV in 1999. Since its development, ArboNET has expanded to include many other arboviruses of public health importance. ArboNET is an electronic surveillance system administered by CDC’s Division of Vector-Borne Diseases. Human arboviral disease data are reported from all states, territories, and freely associated states. In addition to human disease cases, ArboNET maintains data on arboviral infections among human viremic blood donors, non-human mammals, sentinel animals, dead birds, and mosquitoes.

Data Collected. Variables collected for human disease cases include patient age, sex, race, and county and state of residence; date of illness onset; case status (i.e., confirmed, probable, suspected, or not a case); clinical syndrome (e.g., encephalitis, meningitis, or uncomplicated fever); whether illness resulted in hospitalization; and whether the illness was fatal. Cases reported as encephalitis (including meningoencephalitis), meningitis, or acute flaccid paralysis are collectively referred to as neuroinvasive disease; others are considered non-neuroinvasive disease. Acute flaccid paralysis can occur with or without encephalitis or meningitis. Information regarding potential non-mosquito-borne transmission (e.g., blood transfusion or organ transplant recipient, breast-fed infant, or laboratory worker) and recent donation of blood or solid organs should be reported if applicable. Clinical symptoms and diagnostic testing data can also be reported.

Blood donors identified as presumptively viremic by nucleic acid amplification test (NAAT) screening of the donation by a blood collection agency are also reported to ArboNET. Case definitions have been developed for the purposes of national surveillance. The date of blood donation is reported in addition to the variables routinely reported for disease cases.

Arboviral disease in non-human mammals (primarily horses) and infections in trapped mosquitoes, dead birds, and sentinel animals (primarily chickens) are also reported to ArboNET. Variables collected for non-human infections include species, state and county, and date of specimen collection or symptom onset. The total number of mosquitoes or birds tested weekly can also be reported by county and species.

Detailed descriptions of all variables collected by ArboNET and instructions for reporting are included in the ArboNET User Guide, which can be requested from DVBD by phone (970-261-6400) or email (

Data Transmission. Jurisdictions can transmit data to ArboNET using one or more of four methods supported by DVBD: 1) jurisdictions that have a commercially- or state-developed electronic surveillance system can upload records from their system using an Extensible Markup Language (XML) message; 2) jurisdictions can upload records from a MicrosoftÒ Access database provided by CDC DVBD using an XML message; 3) jurisdictions may enter records manually using a CDC website (; or 4) jurisdictions can report cases using an HL-7 message via the CDC National Electronic Disease Surveillance System (NEDSS) and DVBD will download records directly from NEDSS to ArboNET. ArboNET data are maintained in a MicrosoftÒ Structured Query Language (SQL) ServerÒ database inside CDC’s firewall. Users can access data via a password-protected website but are limited to viewing data only from their own jurisdiction. The ArboNET website and database are maintained by CDC information technology staff and are backed up nightly.

Dissemination of ArboNET Data. CDC epidemiologists periodically review and analyze ArboNET surveillance data and disseminate results to stakeholders via direct communication, briefs in Morbidity and Mortality Weekly Reports and Epi-X, comprehensive annual summary reports, and DVBD’s website. CDC also produces maps of domestic and exotic arboviral activity, which are then posted on a website ( Surveillance reports are typically updated biweekly during the transmission season and monthly during the off-season. A final report is usually released in the spring of the following year. CDC provides limited-use ArboNET data sets to the general public by formal request. Data release guidelines have been updated to be consistent with those developed by CDC and the Council of State and Territorial Epidemiologists (CSTE).

Limitations of ArboNET Data. Human surveillance for arboviral disease is largely passive, and relies on the receipt of information from physicians, laboratories, and other reporting sources by state health departments. For viruses that can cause neuroinvasive disease, neuroinvasive disease cases are likely to be consistently reported because of the substantial morbidity associated with this clinical syndrome. In comparison, non-neuroinvasive disease cases are inconsistently reported because of a less severe spectrum of illness, geographic differences in disease awareness and healthcare seeking behavior, and variable capacity for laboratory testing. Surveillance data for fever cases associated with neuroinvasive arboviruses should be interpreted with caution and generally should not be used to make comparisons between geographic areas or over time. Accordingly, ratios of reported neuroinvasive disease cases to non-neuroinvasive disease cases should not be interpreted as a measure of virulence in an area.

ArboNET does not routinely collect information regarding clinical signs and symptoms or diagnostic laboratory test results. Therefore, misclassification of the various syndromes caused by arboviruses cannot be detected. In addition, ArboNET does not routinely collect information regarding the specific laboratory methods used to confirm each case. Although serologic assays are relatively specific, false-positive results and cross-reactions occur between related viruses (e.g., flavivirus, such as West Nile, St. Louis encephalitis, and dengue viruses, or California serogroup viruses, such as La Crosse and Jamestown Canyon viruses). Positive IgM results should be confirmed by additional tests, especially plaque-reduction neutralization. However, such confirmatory testing often is not performed. While the electronic mechanisms for data transmission allow for rapid case reporting, the inclusion of both clinical and laboratory criteria in the surveillance case definition creates delays between the occurrence of cases and their reporting. Provisional data are disseminated to allow for monitoring of regional and national epidemiology during the arboviral transmission season. However, these reports generally lag several weeks behind the occurrence of the cases comprising them, and the data may change substantially before they are finalized. For this reason, provisional data from the current transmission season should not be combined with or compared to provisional or final data from previous years.

The collection and reporting of non-human surveillance data are highly variable among states (and even between regions within states) and changes from year to year. Because of this variability, non-human surveillance data should not be used to compare arboviral activity between geographic areas or over time.

For more information about ArboNET, please contact the Division of Vector-Borne Diseases by phone: 970-261-6400 or email: