Research and analysis

HPR volume 15 issue 16: news (30 September)

Updated 19 January 2022

M. chimaera infection associated with cardiopulmonary bypass: an update

Since first reported in 2015, 49 cases of invasive Mycobacterium chimaera infections in patients who underwent cardiac surgery have been identified in the UK. The cases form part of a global outbreak linked to aerosols generated by contaminated heater cooler units (HCUs) used during cardiopulmonary bypass.

As part of the UK investigation, led by PHE in partnership with the NHS, MHRA, Public Health Wales, Health Protection Scotland and the Public Health Agency of Northern Ireland, enhanced surveillance was established in 2015. Cases have continued to be reported in the ensuing years, reflecting the long latent period associated with these infections and the challenges in implementing control measures without disruption to life-saving surgery. Of the 49 cases identified in the UK, 46 underwent surgery in England, 2 in Wales and 1 in Northern Ireland. Cases were linked to surgery in 23 different cardiac centres (NHS and independent sector), with the majority (43) of cases associated with cardiac valve repair or replacement surgery. The number of cases diagnosed each year has fallen since 2017 (10), with the most recent case diagnosed in 2021. The earliest implicated surgery was performed in 2006 and the most recent in 2017. The median interval between surgery and diagnosis was 2 years (IQR 15 to 35 months); a case has been identified who developed symptoms over 12 years after surgery. Thirty-three of the 49 cases are known to have died.

Monitoring of ongoing risk focused on patients undergoing heart valve surgery given the higher risk for these patients. Of cases undergoing such procedures between 2007 and 2020, the highest risk was in 2014, with 0.7 cases arising per 1,000 patients. Between 2007 and 2017, approximately 167,000 patients underwent valve repair or replacement surgery in the NHS in England according to Hospital Episode Statistics, with estimated risk of 0.2 cases of M. chimaera infection per 10,000 patients (or 1 in 5,000). The risk to patients substantially fell after 2014 reaching 0.06 per 1,000 patients in 2017.

Given the long latency period, it is not possible to ascertain at which point the risk is no longer present as further patients who underwent surgery in recent years may yet be diagnosed. However, no infection in patients who underwent surgery since 2018 have to date been reported. Infection and cardiothoracic specialists should maintain suspicion of possible M. chimaera infection in patients who have had exposure to heater cooler units and who present with a compatible clinical syndrome, and undertake mycobacterial culture accordingly.

Specialist advice can be sought from the nearest reference service as follows:

• National Mycobacterial Reference Service (England)
  • London: nmrs-south@nhs.net
  • Birmingham: uhb-tr.nmrs@nhs.net
• Wales Centre for Mycobacteria: matthijs.backx2@wales.nhs.uk or Jason.Evans@wales.nhs.uk
• Northern Ireland Mycobacterium Reference Laboratory: NIPHL
• Scottish Mycobacteria Reference Laboratory: Loth.Smrl@nhslothian.scot.nhs.uk

All isolates of mycobacteria from suspected or definite cases should be submitted to the respective national mycobacterial reference services.

Non-tuberculous mycobacterial infections in patients who have had cardiothoracic surgery or ECMO, or which are strongly linked to HCUs, should continue to be reported to their local health protection team (HPT). The HPT will request information using the Atypical mycobacterial infection diagnosed in 10 years following cardiopulmonary bypass: surveillance form, which will be submitted to the Healthcare-Associated Infection and Antimicrobial Resistance department at PHE Colindale.

Vaccine coverage report: COVER programme first quarterly report for financial year 2021 to 2022

Quarterly vaccination coverage statistics for children aged up to 5 years in the UK (COVER programme): April to June 2021.