CTAD Chlamydia Surveillance System – GOV.UK

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Letter from PHE and NHS Test and Trace to school and college leaders


The CTAD Chlamydia Surveillance System is the new name for the Chlamydia Testing Activity Dataset (CTAD).

CTAD Chlamydia Surveillance System data are used to provide detailed reports at national and local levels on screening coverage, the proportion of chlamydia tests that are positive and the chlamydia detection rate in England.

Public Health England (PHE) uses chlamydia data combined from the CTAD Chlamydia Surveillance System and the GUMCAD STI Surveillance System to report chlamydia testing activity.

CTAD became mandatory in April 2012, replacing the NCSP and the non-NCSP non-GUM (NNNG) data sources of chlamydia data from non-specialist sexual health services (SHSs). These changes mean that data for 2012 onwards are not directly comparable with the data reported in earlier years.


Technical guidance and dataset specifications for laboratories submitting data in compliance with the Standardisation Committee for Care Information (SCCI).

CTAD: specification and technical guidance

Commissioning laboratory testing

PHE encourages commissioners, providers and laboratories to work together to ensure that the data for local CTAD returns are complete. PHE has developed information and other resources to help the commissioning of chlamydia activity data collection.

CTAD: commissioning guidance, 2015 update

CTAD: implementation regional workshop report

CTAD: briefing document and frequently asked questions

Re-submitting retrospective CTAD data

Laboratories are encouraged to resubmit CTAD data for any period (including 2012) to the HIV and STI Web Portal when there has been an improvement in the data quality and completeness since the original submission. These data will be available to registered portal users. Any data resubmitted will be reflected in the next annual data release.

CTAD: data refreshing communication (PHE HIV and STI Web Portal)

CTAD quality

The CTAD data validation process identified 2 main issues that affect local authority level chlamydia data:

  • postcode of residence: to ensure tests and diagnoses are assigned to the correct local authority

  • testing service type: to minimise double-counting between CTAD and GUMCAD and to correctly monitor testing carried out in different settings

Improving data accuracy and completeness will improve the quality of data for different service types.

Submission and reporting deadlines

Submission period Reporting deadline
January to March 2021 Friday 14 May 2021
April to June 2021 Friday 13 August 2021
July to September 2021 Friday 12 November 2021
October to December 2021 Friday 11 February 2022

Resubmissions can be done anytime, please contact CTAD in advance.

Accessing CTAD data

Information on chlamydia and service provision in England is available on:

Information and guidance on sexual and reproductive health at national and local authority level is available on:

Restricted-access reports for monitoring local, regional and national sexual health priorities are available on the HIV and STI web portal (registered NHS and local authority users only):

  • local authority STI and HIV epidemiology reports (LASERs)
  • GUMCAD STI diagnoses and services reports
  • CTAD data quality reports
  • NCSP quarterly data tables
  • chlamydia: re-testing following a positive diagnosis report

The principles for accessing, storing and sharing CTAD data are given in the PHE HIV and STI data sharing policy.

Data request form

Other data may be requested by completing the CTAD: data request form and sending this to ctad@phe.gov.uk

The data team will aim to provide the data within 2 weeks but this may be longer during busier periods such as after the annual data release.

Changes since 2012 in the chlamydia data

Since the Information Standard (ISB 1538) was approved in 2011 by the Information Standards Board for Health and Social Care (ISB), a number of amendments to the dataset are required to reflect changes in health boundaries and service delivery and improve data quality. This Information Standard has been revised to include one new item, an additional coding option within an existing item and retirement of one item. In addition, there are some minor changes to the NHS Data Dictionary coding options to 2 existing data items. These changes have now been accepted by the Standardisation Committee for Care Information (SCCI) – the standard is SCCI1538.

Background documents

CTAD: Information Standard Notice (December 2014)

CTAD: ISB main submission document

CTAD Phase 1: pilot report

CTAD Phase 2: pilot report

CTAD: National Information Governance Board (NIGB) approval

CTAD: understanding the changes in 2012 chlamydia data

For further information, including access permission to the HIV and STI web portal, contact the CTAD helpdesk at ctad@phe.gov.uk

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