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What is Case Surveillance?
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Case surveillance is foundational to public health practice. It helps us to understand diseases and
their spread and determine appropriate actions to control outbreaks. Case surveillance occurs
each time public health agencies at the local, state, or national levels collect information about a
case or person diagnosed with a disease or condition that poses a serious health threat to
Americans. These diseases and conditions include
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infectious diseases, such as coronavirus disease 2019 (COVID-19);
foodborne outbreaks, such as E.coli; and
noninfectious conditions, such as lead poisoning.

View or Download Our Materials
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Infographic PDF pdf icon[341 KB, 2 Pages, 508]
Overview Fact Sheet pdf icon[162 KB, 2 Pages, 508]
Overview Video (YouTube)

Case surveillance starts at local, state, and territorial public health departments. Local laws and
regulations specify which diseases and conditions must be reported. The health departments
work with healthcare providers, laboratories, hospitals, and other partners to get the information
needed to monitor, control, and prevent these reportable diseases and conditions in their
communities.
Health departments also notify CDC about certain conditions so we can track them for the whole
country. CDC monitors about 120 of these notifiable diseases and conditions at the national
level. This important step helps protect the health of individual communities and the nation.
Following standard case definitions, case surveillance captures information that public health
officials can use to understand where diseases are occurring, how they can be prevented, and
which groups are most heavily impacted. This information includes:
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who is affected—the demographic, clinical, and epidemiologic characteristics;
where they are affected—the geographic distribution of disease; and
how they are affected—the course of clinical illness and care received.

Reportable or Notifiable: What’s the Difference?

Reportable or Notifiable: What’s the Difference?
Reportable Diseases and Conditions
state or territory sets local laws
and rules for which diseases and
conditions must be reported.

Notifiable Diseases and Conditions

• Each

• The Council

• Healthcare professionals,

• States

• Public health

• Case records

• This

• CDC

• The list

• The list

laboratories,
hospitals, and other providers must
tell public health departments when a
person is diagnosed.
departments collect
information about the person and
how they became ill.
information is used to locate the
source of an outbreak and prevent
spread.
of diseases and conditions can
change every year.

of State and Territorial
Epidemiologists and CDC identify the
list of notifiable diseases and
conditions.
voluntarily inform CDC when a
person meets certain criteria to
become a case.*

do not contain personally
identifiable information.
uses data to monitor, measure, and
alert individual communities or the
nation to outbreaks and other public
health threats.
of about 120 diseases and
conditions is updated every year.

About the National Notifiable Diseases Surveillance System
CDC conducts case surveillance through the National Notifiable Diseases Surveillance System
(NNDSS). In the case surveillance process, about 3,000 health departments gather and use data
on disease cases to protect their local communities. Through NNDSS, CDC receives and uses
these data to keep people healthy and defend America from health threats.
CDC programs responsible for national surveillance, prevention, and control of infectious and
noninfectious conditions are found in the following centers:
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Center for Global Health (CGH);
National Center for Chronic Disease Prevention and Health Promotion (NCCDPHP);
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID);
National Center for Environmental Health (NCEH);
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention (NCHHSTP);
National Center for Immunization and Respiratory Diseases (NCIRD); and

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National Institute for Occupational Safety and Health (NIOSH).

These programs collaborate with the Council of State and Territorial Epidemiologists to
determine which conditions reported to local, state, and territorial public health departments are
nationally notifiable. The Council of State and Territorial Epidemiologists brings together
disease and surveillance experts at CDC and in the health departments to determine what types
of data should be included in national notifications.
NNDSS receives, processes, and provides data on national notifiable diseases to programs across
CDC. The programs use these data to do the following:
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recognize disease outbreaks;
track the spread of disease at the state, regional, and national levels;
identify geographic areas of concern and inform state decision makers;
help state and local public health departments better control disease by identifying groups
most at risk; and
evaluate and fund disease control activities.

By the Numbers
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About 120 diseases are under surveillance through NNDSS, including infectious
diseases, bioterrorism agents, sexually transmitted diseases, and noninfectious conditions.
Nearly 2.7 million disease cases are reported through NNDSS each year.
About 3,000 public health departments send disease data to 60 state, territorial, and
other public health departments, who then send the data to CDC.
100% of the American population is protected through NNDSS.

NNDSS Modernization
As technology, data, and exchange standards evolve, CDC is strengthening and modernizing the
infrastructure that supports NNDSS. As part of the Data Modernization Initiative, CDC is
enhancing the ability of NNDSS to provide comprehensive, timely, and high-quality data for
public health decision making. Through this multi-year initiative, CDC is making the NNDSS
technological infrastructure more robust so that it is based on interoperable, standardized data
and exchange mechanisms.

More About Case Surveillance and NNDSS

How We Conduct Case-Based Disease Surveillance
Learn about the process and data systems that NNDSS uses to collect national notifiable disease
case data.
Read More

History and Modernization of Case Surveillance
View major milestones in the advancement of notifiable disease case surveillance.
Read More
* OMB No. 0920-0728 (Expiration Date: 05/31/2025) The public reporting burden of this collection of information
is estimated to average 20 minutes per response for states, cities, and territories that automate case notification, 2
hours for states and cities that do not automate, and 20 minutes for territories and freely associated states that do not
automate. This includes the time for reviewing instructions, searching existing data sources, gathering and
maintaining the data needed, and completing and reviewing the collection of information. An agency may not
conduct or sponsor, and a person is not required to respond to all collection of information unless it displays a

currently valid OMB control number. Send comments regarding this burden estimate or any other aspect of this
collection of information, including suggestions for reducing this burden to – CDC/ATSDR Reports Clearance
Officer; 1600 Clifton Road NE, MS D-74, Atlanta, Georgia 30329 ATTN: PRA (0920-0728).

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Page last reviewed: February 25, 2022
Content source: Division of Health Informatics and Surveillance
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