Worries grew in Germany Tuesday about infections caused by a strain of the E. coli bacterium after authorities reported the death of an 83-year-old and a "very unusual" number of cases. The health ministry in the northern state of Lower Saxony said that an autopsy was being carried out on the woman who died Saturday after suffering from bloody diarrhoea for a week. The woman was confirmed to have been infected with enterohaemorrhagic E. coli (EHEC), but tests were being carried out to see if this led to her death, the ministry said in a statement. The Robert Koch Institute (RKI), the national disease-control and prevention agency, said that over the past two weeks more than 80 cases of potentially fatal haemolytic uraemic syndrome (HUS), caused by EHEC, have been recorded. "The number of serious cases in such a short time period is very unusual, and the age groups affected is also untypical," the RKI said in a statement. Currently it is mostly adults, in most cases women, who have been affected, whereas previous outbreaks have been in children, the RKI said. The majority of the cases are in northern Germany so far. In 2010, for example, there were 65 cases of HUS, of which only six were aged 18 years or over. There were two fatalities. According to the World Health Organization's website, HUS is characterised by acute renal failure and blood problems, with a fatality rate of between three and five percent. It can also cause seizures, strokes and coma. Around 10 percent of patients infected with EHEC could develop HUS, the WHO said. Every year there are around 1,000 suspected EHEC infections in Germany, the RKI said. It added that the source of the EHEC outbreak had not yet been identified and advised people to heat food and observe proper standards of hygiene.