Q&A for Implementation

Questions and answers about implementing message mapping guides (MMGs) for HL7 case notifications to NNDSS.


Q: Which data elements are needed by CDC to define a unique case?

A: Two data elements are used together to define a unique case for HL7 case notification messages transmitted to the Message Validation, Processing, and Provisioning System (MVPS):

  • Local Record ID (INV168 in OBR-3)
  • National Reporting Jurisdiction (77968-6).

The values of these two data elements must remain the same when sending updates on a unique case.  Any changes to these data elements will cause the addition of a new case to the CDC database. The “HL7 Implementation Notes” in the generic version 2 MMG also includes the notes about the use of these two variables in defining a unique case at CDC.

For more information, please see this document: https://ndc.services.cdc.gov/wp-content/uploads/2021/02/

Q: For coded with exceptions (CWE) and coded element (CE) data types, does the standard code need to be placed in the first triplet and does the local (alternative) code have to be placed in the second triplet?

A: No. The standard and local codes can be sent in either the first or second triplet. When CDC processes the data, the triplets will be scanned to identify the standard code and will validate the value against the standard.

Q: The message mapping guide includes a coded data element that my reporting jurisdiction captures as a text field instead of a coded data element. What should I do?

A:  The coded value of “other” (or “other. XX”) should be included in the first triplet if it is available in the value set, in addition to sending the corresponding text in the ninth component of the CWE data element.  If the first triplet is left blank and text is still sent in the ninth component, the text must specify a value from the specific coded value set. Also, if a coded value cannot be sent in the first triplet, please discuss the reason for not sending a coded value with the CDC program.

Q: The order of the information in the test scenarios does not match the order of the information in my surveillance information system. What should I do?

A: Please enter the information into the correct fields in your surveillance information system.  You can reorder the data elements in the test scenario to match the order of the data elements in your surveillance information system to help facilitate the data entry process.

Q: Can Object Identifiers (OIDS) be sent in CE and CWE data elements rather than identifiers from HL7 table 0386?

A:  Either OIDs or data from HL7 table 0396 can be used. In the latest version of the PHIN Message Structure Specification, the CE.3 and CWE.3 “Name of Coding System” and CE.6 and CWE.6 “Name of Alternate Coding System” components maximum length was increased to 199 to allow the use of OIDs instead of Table 0396 code system code, if desired by the implementer.

Q: If a reporting jurisdiction does not have the resources to send both laboratory interpretive data (in the Epi observation request [OBR] segment) and laboratory-associated data (in the Lab OBR segment), which is higher priority?

A: The laboratory interpretive data in the Epi OBR is the priority for the HL7 case notifications.  If a reporting jurisdiction can send both types of data that would be helpful. However, the reporting jurisdiction should not send optional lab findings in the Lab OBR instead of interpretive laboratory data in Epi OBR.

Data Submission and Updates

Q: When should jurisdictions send case notifications—as soon they have information on the case or at the end of the week?

A: CDC encourages jurisdictions to send case notifications as soon as they have information on the case. This will make the data available to the CDC programs sooner. Jurisdictions can always send updates as they receive more information on a case.

Q: Can jurisdictions use the HL7 MMGs to send in summary case notifications for specific diseases?

No. The HL7 MMGs are intended for transmitting individual case notifications. Jurisdictions should transition from sending summary counts to sending individual case notifications.

Q: Is CDC using snapshot processing of HL7 case notification messages?

A: Yes. HL7 case notification messages are stored as separate messages, and more recent messages do not overwrite nor update previous messages. The most recent case notification messages will be used by the CDC programs.

Q: How do I update information on a previously submitted case?

A: To update the information on a previously submitted case, update the information in your surveillance system and then re-send the case. The Notification Result Status (in OBR-25) should be set to “C” to indicate a correction. If the case classification changes as a result of the new information, please remember to update the case classification status (e.g., confirmed, probable, suspected, not a case.) The updated record will supersede the previous HL7 case notification sent to CDC.  When sending updates, please be careful not to change the data elements that CDC uses to define a unique case.

The following data element is used by MVPS to identify the most recent notification for a case:

  • Date Reported (NOT106 in OBR-22).

In the unique situation where a state is asked to retransmit a previously sent message or batch, MVPS uses MSH-7 to identify the most current record.

Q: How do I indicate that a previously transmitted case is no longer a case?

A: If you determine that a previously sent case should not be counted as a case, send an updated case notification using one of the following methods:

Preferred Method: Resend the case with case classification status data element ‘77990-0’ = “Not a Case” and Notification Result Status (OBR-25) = “C” to indicate this is a correction.

Alternate Method:  Resend the case with case classification status data element ‘77990-0’ = “Not a Case” and Notification Result Status (OBR-25) = “X” to indicate this case is “rescinded.”

Alternate Method for jurisdictions unable to send case classification status of “Not a Case”: Regardless of the value transmitted in the case classification status, resend the case with Notification Result Status (in OBR-25) = “X” to indicate this case is rescinded.

The updated record will supersede the previously sent case notification.  CDC programs will be informed that notifications with a case classification status of “Not a Case” or Notification Result Status of “X’ should not be included in case counts.

When sending updates, please be careful not to change the data elements that CDC uses to define a unique case.

Generic v2 Usage

Q: What diseases can be sent by using the generic v2 notification or other HL7 notifications?

A: The NNDSS Event Code List available at Event Codes and Other Surveillance Resources indicates the conditions (and their respective event codes) that should be sent to NNDSS by using the generic v2 HL7 case notification and other HL7 case notifications. As new disease-specific HL7 case notification formats are developed, they will be added to this document.

The “Event Codes” worksheet in the National Notifiable Diseases Surveillance System Event Code List has a “Preferred New HL7 Message” column and an “Alternative Message.” These columns can be filtered by the type of case notification message. For example, if the “Preferred New HL7 Message” column is filtered by “Generic,” then the conditions that require only the generic v2 case notifications will be listed. The “Alternative Message” column includes information about when the generic message (by itself) or the generic message plus a case report form can be used. Alternatively, if the “Preferred Mechanism” column is filtered by “Sexually Transmitted Diseases,” it shows the list of STD conditions that should be sent by using both the STD MMG data elements and the generic v2 data elements.

Q: Are all elements in the generic v2 MMG required?

A: Not all the data elements in generic v2 are required, but jurisdictions are strongly encouraged to collect and send all of this information. The column named “CDC Priority” indicates the prioritization of the data element by the CDC surveillance program. The following data element priorities are used in the MMGs.

  • R – This data element is mandatory for sending a message. If the required data element is not present, the message will be rejected. The required data elements alone are not sufficient for national surveillance purposes.
  • 1 – Highest priority for reporting. These data elements are critical for national surveillance activities. A jurisdiction’s data collection system should be modified to collect Priority 1 data elements. If this data element is not currently collected and available to send, jurisdictions should discuss with the CDC program whether they can onboard without that element being available and included in the messages. Some CDC programs may request a plan addressing future inclusion of these data elements, if jurisdictions are not able to collect and transmit at onboarding.
  • 2 – High-priority data element that will support national surveillance activities. If this data element is not currently collected and available to send, a jurisdiction should plan to update its data collection system. Some CDC programs may request a plan addressing future inclusion of these data elements, if jurisdictions are not able to collect and transmit at onboarding.
  • 3 – Lower priority data element that should be considered for inclusion in the surveillance system and case notification. Jurisdictions should send if currently collected in the system.

Regardless of whether a data element is priority 1, 2, or 3, jurisdictions should send all the requested data elements that they collect in their surveillance information systems. CDC encourages jurisdictions to enhance their surveillance systems to capture all of the data elements requested in the MMG.

Q: Can jurisdictions continue to submit information in the generic v1 MMG?

A: CDC encourages jurisdictions to transition to new guides as soon as possible after they are published as final because the new data elements are important for notifiable disease surveillance.

Q: Can jurisdictions use the generic v2 MMG to send notifications for conditions that have extended data in the National Electronic Telecommunications System for Surveillance (NETSS)?

A: Conditions being sent to CDC through NETSS with disease-specific data cannot be sent by using an HL7 message until there is a disease-specific MMG to complete the case notification and the jurisdiction has been approved to send the disease-specific HL7 case notification.

Jurisdictions should use the National Notifiable Diseases Surveillance System Event Code List, available at Event Codes and Other Surveillance Resources to identify which conditions should be sent by using each of the HL7 MMGs.

Q: Do jurisdictions need to send generic v2 messages in addition to the disease-specific message?

A: When there is a disease-specific MMG, the case notification should include the disease-specific data elements from the disease-specific MMG in combination with the data elements from the generic v2 MMG.


Q: What is the NNDSS onboarding process?

A: Onboarding ensures that jurisdictions transmit data in compliance with the NNDSS message mapping guide requirements and that CDC programs are confident in the quality of the data that they are receiving.

Detailed information about the onboarding process and how a jurisdiction can indicate readiness to onboard for an MMG is provided in the HL7 Implementation and Onboarding section.

Data Reconciliation

Q: How is data reconciliation done with the HL7 case notifications?

A: With MVPS, jurisdictions receive an acknowledgment confirming receipt and parsing of messages. A dashboard summarizes data sent by jurisdictions, including the details of messages received and processed by CDC, and it flags any warnings or errors. Jurisdictions will be able to identify problems and submit corrections to reconcile the data as needed throughout the year.

Q: Will CDC program areas adhere to receiving data in this new way or will they still ask for jurisdiction data in Excel or other files?

A: CDC is working to eliminate the duplication of data requested by CDC in various formats.

Q: How long will jurisdictions be expected to send notifications for some diseases in the HL7 format and for other diseases in the old format?

A: NNDSS is working with CDC programs to ensure that there are HL7-based MMGs in place for all conditions that are generally sent through NNDSS. The only NNDSS conditions for which no MMGs are currently planned are HIV infection and animal rabies. 

The period of time during which a jurisdiction may need to send case notification messages in HL7 for some conditions and in an old format for other conditions will depend on the speed at which the jurisdiction implements the HL7-based messages. Jurisdictions should develop and adhere to a plan to implement HL7 messages as they become available and to retire the old format feeds. CDC can provide technical assistance to help with the development of those plans and with implementation of the HL7 messages.

Also see:

Supporting Documents for Implementation