Doctors in Halland in western Sweden are unable to concrete prognosis for the woman who is reported to be suffering from kidney problems and is being treated with a dialysis and respirator.
"How long the dialysis treatment will take is difficult to say. It could be a couple of days, a couple of weeks or become a chronic disease," said doctor Mats Erntell.
The Local reported earlier on Monday that six more Swedes have been infected by the EHEC bacteria, bringing the total number of cases in Sweden to 39.
The Swedish Institute for Communicable Disease Control (Smitskyddsinstitutet – SMI) believes that all cases of the diseases reported so far in Sweden originated in Germany and there are no indications thus far that the disease is spreading within Sweden.
Nevertheless, the agency said in a statement on Sunday that the number of reported cases could very well increase in the coming days.
Of the 36 people who have been affected by the E. coli outbreak, 13 are being treated for the haemolytic-uremic syndrome (HUS) complication that causes patients serious trouble and can be fatal.
Several of the patients have been admitted to intensive care units and are receiving dialysis treatment.
German health authorities have confirmed two HUS-related fatalities and are investigating eight additional deaths believed to have been caused by the complication.
So far, 300 people in Germany have contracted the disease in recent weeks.
Sweden's SMI has also found that two of the most serious Swedish cases of the disease have come from the same rare EHEC serotype O104 found in Germany, and expects further analyses to confirm the suspected ties to the German outbreak.
The agency is also urging people visiting northern Germany to follow advisories issued by the German health authorities to avoid eating uncooked cucumbers, lettuce, and tomatoes.
Outbreaks of EHEC are not that common in Sweden. Smaller outbreaks are sometimes connected to farms, wells, day care centres and restaurants.
The largest outbreak to date in Sweden was in 2005 when 135 cases, of which 11 developed the complication HUS, occurred in southern Sweden.