Two people have died in the US after being affected by the cyclospora outbreak that often causes "explosive diarrhoea".
Lettuce from Mexico served in Taco Bell restaurants is believed to be to blame, though the Federal Drug Administration (FDA) is looking at other potential sources.
The two deaths - the first linked to the current US outbreak - were announced by Michigan's health department on Monday.
They said both people had underlying health conditions that may have been significant.
Nine states have been affected so far and 11,000 cases have been identified in Michigan alone - up from 461 in Friday's update.
Nearly 200 people have been hospitalised in the state.
The cyclospora parasite spreads through food or water contaminated with human faeces.
This often happens when produce, such as salad leaves and unpeeled fruit, is washed with contaminated water.
Taco Bell has said it's no longer using iceberg lettuce from Taylor Farms - the company that produced it - while other similar lettuce products have been recalled.
"Explosive diarrhoea" is one of the main symptoms of cyclospora, according to the UK Health Security Agency (UKHSA).
Others include abdominal cramping, bloating, nausea, flatulence, low-grade fever, loss of appetite and weight loss.
The UKHSA warned last week over a "sharp rise" in infections in holidaymakers returning from Mexico. Over 130 cases were recorded between 30 April and 15 July - significantly higher than the annual average of 93.
Read more from Sky News:
Wildfire emergency declared in Washington state
Netflix sued for $105m over stolen Nicolas Cage film
It advises travellers to Mexico to only drink bottled water and make sure their food is thoroughly cooked "even when staying in high-end all-inclusive resorts".
It also advises skipping salad items, berries, unpeeled fruit and herbs. Ice in drinks is another potential source of infection.
The NHS says the infection normally subsides "within a few days or weeks" and that sufferers should try to stay hydrated by having lots of fluid.
(c) Sky News 2026: Two die as cases of 'explosive diarrhoea' infection cyclospora surge in Michigan
Andy Burnham blocks early prison release for rapists - but PC Andrew Harper's widow slams 'betrayal' as husband's killers to be freed early
How Gianni Infantino will be framing his battle to remain FIFA president
Thousands of migrants remain in Ceuta after deadly mass rush from Morocco
Woman who stole £300k from pensioner before Sky News tracked her down in Tenerife is jailed
Vampire fan given hospital order after putting animal body parts in churches
