NHS sandwiches have killed two more patients, bringing the death toll to five, Public Health England (PHE) has confirmed, as it continued to investigate whether more people have died at dozens of trusts.Last week, public health officials said three seriously ill patients had died, and three more infected, after eating food which contained the deadly bacteria listeria.Another of those original six has since died, PHE confirmed on Friday along with a fifth person who was not initially linked to the outbreak. Post-mortem DNA analysis showed the critically ill patient had been infected with the same bacterial strain.Two other hospital patients were also infected, bringing the overall total to nine and the NHS is now running genomic tests on people who died over the past two months amid concerns some of the deaths were caused by the food poisoning outbreak..Dr Nick Phin, Deputy Director of the National Infection Service at PHE, said: “To date, there have been no patients linked to this incident outside healthcare organisations, but we continue to investigate.“Swift action was taken to protect patients and any risk to the public is low. PHE is continuing to analyse all recent and ongoing samples of listeria from hospital patients to understand whether their illness is linked to this outbreak.” Dr Colin Sullivan, Chief Operating Officer at the FSA said: “Our sympathies remain with the families of the patients who have tragically passed away.“We have taken action along with local authorities to minimise the risk based on the evidence so far. The FSA will continue to investigate the cause of the outbreak to prevent a reoccurrence.” The original deaths occurred at Manchester Royal Infirmary and Aintree Hospital in Liverpool. PHE is carrying out its investigations alongside the Food Standards Agency (FSA), NHS England and NHS Improvement, as well as partner organisations in Scotland and Wales. A spokesman for The Good Food Chain said: “Our thoughts and deepest sympathies are with the families of those who have died and anyone else who has been affected by this outbreak. The underlying cause of it remains unclear.”Experts have warned that more people could be infected because of the long incubation period of listeria. The bacteria can lie dormant for up to 70 days and sandwiches were not withdrawn from the NHS until May 25th after investigators realised they had been eaten by all three of the victims.Some 43 out of the 135 NHS trusts were supplied by The Good Food Chain and they have been placed on alert for cases of listeriosis, which can lead to deadly sepsis and meningitis. In pregnant women it can also cause miscarriage and be passed on to the unborn child. All those who died had been given sandwiches supplied by The Good Food Chain, a company based in Stone, Staffordshire, whose Whole Lotta Good brand was developed specifically for hospitals.The company, which also supplies some schools, has voluntarily ceased production while an investigation continues, as has the firm which supplied its meat, Northern Country Cooked Meats, which operates out of Salford. Show more Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.