National Electronic Telecommunications System for Surveillance

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What Is NETSS?

The National Electronic Telecommunications System for Surveillance (NETSS) is a computerized public health surveillance information system that provides the Centers for Disease Control and Prevention (CDC) with weekly data regarding cases of nationally notifiable diseases.

What is a notifiable disease? A notifiable disease is one for which regular, frequent, timely information on individual cases is considered necessary to prevent and control that disease. The list of notifiable diseases varies over time and by state. The list of nationally notifiable diseases is reviewed and modified by the Council of State and Territorial Epidemiologists (CSTE) and CDC once each year and is available on the Internet at

What kind of information is reported through NETSS, and how often is it reported?

Core surveillance data –date, county, age, sex, and race/ethnicity –and some disease-specific epidemiologic information for nationally notifiable diseases and for some nonnotifiable diseases are transmitted electronically by the states and territories to CDC through NETSS each week.

Are all cases of disease reported to CDC?

Completeness of reporting varies by disease and state and can be influenced by – 

• the type and severity of illness;
• whether treatment is sought in a health-care setting;
• diagnosis of an illness;
• availability of diagnostic services;
• the disease-control measures in effect;
• the public's awareness of the disease; and 
• the resources, priorities, and interests of state and local officials responsible for disease control and public health surveillance.

Are the data complete? Colleagues in state and local health departments and CDC staff make every attempt to obtain complete demographic information associated with nationally notifiable cases of disease. However, sometimes data (particularly the variables of race and ethnicity) are not available for certain cases of disease.

Does the CDC database contain personal identifiers?

Personal identifiers such as name and address are never transmitted to CDC in reports of cases of notifiable disease. Release of data is restricted because CDC and CSTE are required to protect the confidential nature of the data.

Does CDC mandate participation in NETSS?

No. Each state or territory regulates its reporting of nationally notifiable diseases.

How are the data used? 

Weekly reports of national morbidity data are essential for public health managers and providers to rapidly identify disease epidemics and understand patterns of disease occurrence. The usefulness of these weekly reports is enhanced by the case-specific information included in NETSS reports. Changes in age, sex, race/ethnicity, and geographic distributions can be monitored and investigated as necessary.

How does CDC receive reports of notifiable diseases?

Through NETSS, CDC receives reports of notifiable diseases from the 50 state health departments, New York City, the District of Columbia, and five U.S. Territories. These reports are initiated when health-care providers suspect or diagnose a case of disease that is notifiable in their state. They are to report the case by mail, telephone, or facsimile, to the local, county, or state health department. Clinical laboratories also report results consistent with reportable diseases. When a case of disease is reported at the local level, staff members in the local or county health department implement control measures as needed and forward the report to the state health department.

Who operates NETSS?

• develop, test, customize, install, and update computer software for use in state and territorial health departments;
• develop and implement software to validate data sent to NETSS;
• identify incomplete records, transmission errors, and deviations from expected numbers;
• provide technical support to users; and
• convey specifications for record formats on an as-needed basis.

How can the public obtain current updates of data regarding notifiable diseases?

Many public and academic libraries, particularly those at medical schools and schools of public health, maintain copies of documents that contain information regarding notifiable diseases. Provisional weekly reports of notifiable diseases are published in CDC's Morbidity and Mortality Weekly Report (MMWR). Final, corrected data are published in the annual MMWR Summary of Notifiable Diseases, United States. These publications are available in paper form through paid subscriptions from Massachusetts Medical Society, 860 Winter Street, Waltham, MA 02451-1413 (718-893-3800). MMWRs and data regarding case numbers can be searched online at http://www.cdc.gov

Where can the public find other national notifiable disease data? Notifiable disease statistics are also available from CDC's National Center for Health Statistics in its publication, National Vital Statistics Reports (formerly, Monthly Vital Statistics Reports). Issues of National Vital Statistics Reports are available at many medical or public libraries and on the Internet at http://www.cdc.gov/nchswww/.

Must I be located in a state health department to use NETSS?

Only designated staff in state and territorial health departments or in the New York City or District of Columbia health departments can transmit data to CDC through NETSS. In some states, city and county staff enter data that will ultimately be transmitted to CDC, but the weekly transmission of all reported data is overseen by the appropriate state or territorial health department staff.

What computer software must I use to transmit data?

NETSS does not require the use of a specific computer software program. However, data must be transmitted in ASCII (American Standard Code for Information Interchange) format, which allows the NETSS system to integrate data from surveillance systems throughout the United States

Are the data restricted? Yes. To protect the confidentiality of NETSS data, CDC adheres to the CSTE Data Release Policy, which regulates dissemination of the data.

What is the difference between“provisional weekly data”and“final, corrected data”?

Provisional weekly data include only the data reported to CDC each week throughout the year. At year's end, staff in state and territorial health departments correct the accumulated data. The result is final, corrected data, which are published each fall in CDC's MMWR Summary of Notifiable Diseases, United States.

What causes increases or decreases in the numbers of cases from one reporting period to the next?

Most common causes of fluctuations in the numbers include the following:

• a true increase or decrease in the incidence of a disease;
• a change in the case definition or classification of a disease;
• a new diagnostic test for a disease;or
• batched reporting –reporting all cases at the end of a time period rather than weekly as those cases occur.

How did NETSS originate?

In 1984, CDC, in cooperation with the CSTE and epidemiologists in six states began testing the Epidemiologic Surveillance Project. The project's goal was to demonstrate the effectiveness of computer transmission of public health surveillance data between state health departments and CDC. Computer programs were created that used existing disease surveillance systems to transmit data to CDC on cases of all nationally notifiable diseases. By 1985, the system became a full interactive computer-based disease reporting system, and by 1989, all 50 states had begun participating in the reporting system. The Epidemiologic Surveillance Project was then renamed the National Electronic Telecommunications System for Surveillance (NETSS) to reflect its national scope.

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This page last updated April 7, 2004

United States Department of Health and Human Services
Centers for Disease Control and Prevention
Epidemiology Program Office
Division of Public Health Surveillance and Informatics

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