Care home residents develop more infections and are prescribed more antibiotics than other populations as older people often have a weakened immune system, and living in a care home means that residents are in close proximity so infections can spread more easily. As well as having an impact on their quality of life, frequent infections which require treatment with antibiotics exposes care home residents to anti-microbial resistance which can make infections more dangerous and harder to treat. Other than vaccination and hygiene methods, there are few interventions known to prevent infection in older people living in care homes.

Probiotics are friendly ‘live’ bacteria that are safe and cheap and may help improve the immune system of care home residents and reduce the spread of harmful bacteria. There is some evidence that probiotics can help reduce infections, but the evidence on whether they can prevent infections and reduce antibiotic use in care home residents was limited. We conducted the PRINCESS trial to see if a probiotic taken daily by care home residents reduced antibiotic use by preventing infections compared to residents that received a placebo.

What did the PRINCESS trial involve?

We recruited 23 care homes in England and Wales through the ENRICH network and other routes. Research nurses recruited a total of 310 residents who were aged ≥ 65 years and were willing to give informed consent to take part or who had a consultee to provide advice about participation if they lacked capacity to consent.

They were then randomised to have either a capsule containing a probiotic combination (Lactobacillus rhamnosus GG and Bifidobacterium animalis subsp. lactis BB-12) or a capsule that looked the same but that did not contain probiotic bacteria. Residents were given this daily for 12 months and it could be taken as a capsule, dissolved in liquid, or sprinkled on food. Research nurses, who did not know whether the resident was receiving the probiotic combination or a placebo capsule, visited the care home residents each week to collect relevant information.

We then followed their health and wellbeing for a year to see whether they developed infections and on how many days they had antibiotics. We also asked residents (and/or their carers) about their general health and wellbeing. Residents were also asked to provide blood and other samples, if they were happy to do so.

As trials such as this are not common in care homes, we also asked people about their experiences of taking part. We interviewed 2 family members/friends who had provided advice on behalf of a care home resident about participation (as a consultee) or who experienced the resident’s participation in the trial, and 9 research nurses and 7 care home staff who had been involved in the research activities required to recruit care home residents or collecting research data for the trial.

What did the PRINCESS trial find?

We found that the daily probiotic combination did not significantly reduce the number of days on which the care home residents took antibiotics, with the probiotic group having antibiotics for 12.9 days on average, compared with 12 days for the placebo group. We also found that the probiotics did not significantly reduce the number of infections residents had or how long infections lasted. Residents’ overall health and wellbeing was generally similar between the two groups.

What do these findings mean?

This trial has shown that care home residents may not benefit from taking this probiotic combination each day to reduce antibiotic use and prevent infections. However, the findings may not apply to other probiotics or to older people living outside of UK care homes.

What did care home staff, families and research nurses say about the trial?

Care homes, families and research nurses found the PRINCESS trial to be acceptable, which was partly due to the low-risk nature of the study and how carefully care home residents are monitored. The trial was easier to implement in care homes where managers were more actively engaged and supported the trial. However, all care homes needed ongoing engagement and activity by trained research nurses visiting care homes regularly. The development of good relationships between care home staff and research nurses who were very familiar with the care home setting was key in the effective implementation of the trial.

The full report has been published in the NIHR journal Efficacy and Mechanism Evaluation and can be accessed here: https://doi.org/10.3310/eme08070

Research team

Chief Investigator – Prof Chris Butler, University of Oxford

PRINCESS trial team and co-authors of the report – Cardiff University: Dr Eleri Owen-Jones, Mandy Lau, Dr Dave Gillespie, Helen Stanton, Dr Mandy Wootton, Dr Jane Davies, Alison Edwards, Dr Victoria Shepherd, Dr Rachel Lowe, Prof Kerry Hood, Dr Julia Townson, and Prof Antony Bayer. University of Oxford: Prof Richard Hobbs, Mina Davoudianfar, and Heather Rutter. University of Southampton: Dr Mark Lown, Prof Philip Calder, Vivian Castro Herrera, Prof Michael Moore, Prof Paul Little, Elizabeth Miles, and Prof Nick Francis.

This project was funded by the Efficacy and Mechanism Evaluation (EME) programme, a MRC and National Institute for Health Research (NIHR) partnership.

We would like to thank all the residents, families and care homes who took part in PRINCESS, and the research nurses and networks and public involvement members who supported it.