CTAD Chlamydia Surveillance System

PHE collects data on all chlamydia tests done in England from NHS laboratories and LA/NHS commissioned laboratories, to measure screening activity.


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.

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).

GUMCAD reports chlamydia activity from specialist SHSs including service user Area of Residence. This is used to ensure the most accurate attribution possible of tests and diagnoses from specialist SHSs to local areas.

Several significant changes in the way chlamydia data are reported were made in 2012, including the introduction of CTAD. These changes mean that data for 2012 onwards are not directly comparable with the data reported in earlier years.


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 two main issues that affect local authority level chlamydia data:

  • postcode of residence data: this is needed to accurately attribute tests and diagnoses to the correct local authority. If this is missing, ‘out of area’ tests may be attributed to the local authority for where a patient is tested, rather than where they live

  • testing service type data such as specialist SHSs, sexual and reproductive health services (SRH) and general practice (GP): accurate identification of tests from specialist SHSs is essential to enable the correct combination of CTAD and GUMCAD chlamydia data

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

Submission and reporting deadlines

The time periods for laboratory submission deadlines are:

  • January to March 2018: Friday 11 May 2018
  • April to June 2018: Friday 10 August 2018
  • July to September 2018: Friday 9 November 2018
  • October to December 2018: Friday 15 February 2019
  • resubmissions: anytime, please contact CTAD in advance

Accessing CTAD data

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

  • NCSP annual data tables are available on the PHE website. These present data on chlamydia detection rate and chlamydia testing coverage and related service provision at national levels. Data are also presented in an annual slide set
  • Health Protection Report: latest infection reports. These present data on Routine data and commentary reporting on infectious diseases
  • CTAD reporting tools. These can be used to generate data reports for monitoring local, regional and national public health priorities. The reports, which are available on the HIV and STI web portal are restricted for use by nominated local government, NHS and public health organisations
  • the Sexual and Reproductive Health Profiles. The Sexual and Reproductive Health Profiles have been developed by PHE to support local authorities, public health leads and other interested parties monitor the sexual and reproductive health of their population and the contribution of local public health related systems. Interactive maps, charts and tables provide a snapshot and trends across a range of topics including teenage pregnancy, abortions, contraception, HIV, sexually transmitted infections and sexual offences. Wider influences on sexual health such as alcohol use, and other topics particularly relating to teenage conceptions such as education and deprivation level, are also included
  • local Authority STI and HIV Epidemiology Reports (LASERs). These reports aim to describe STIs and HIV in the local area to inform local Joint Strategic Needs Assessments (JSNAs) so that commissioners can effectively target service provision. LASERs are generated annually and are available to sexual health commissioners and Directors of Public Health. The reports are distributed via local Field Epidemiology Service units
  • laboratory specific quality scorecard reports. These provide data on CTAD data quality specifically on percentage completion of patient postcodes and percentage of testing service type. Reports are generated quarterly and distributed to local Field Epidemiology Service units in order for them to work with relevant contacts to improve the data quality
  • Sexual and reproductive health in England: local and national data. Guidance to help health professionals understand the sexual health data available across England and how to access it.

Data request form:

Other data may be requested by completing the form below and sending this to The data team will aim to provide the data within two weeks but this may be longer during busier periods such as after the annual data release.

Please read the PHE HIV and STI data sharing policy on data access, storage, sharing and confidentiality.

CTAD: data request form

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 two 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

Contact information

For further information, including access permission to the HIV and STI web portal contact the CTAD helpdesk at

Published 1 April 2012
Last updated 12 March 2018 + show all updates
  1. Updated the CTAD submission and reporting deadlines for 2018.
  2. First published.