In the United Kingdom, an unprecedented and large-scale outbreak of diarrheal illnesses caused by the intestinal parasite, Cryptosporidium (also known as Crypto), is currently unfolding.
According to a recent rapid communication published in the journal Eurosurveillance, health officials in the UK have reported a significant increase in Crypto cases since mid-September, with a peak in October that is approximately three times higher than the usual number of cases for this time of year. The outbreak is still ongoing.
The cause behind this extraordinary surge in cases is still unknown. The outbreak has affected almost every region across the four nations of the UK. In their rapid report, the authors, led by officials from the United Kingdom Health Security Agency in London, stated that a single local exposure is an unlikely explanation for the widespread and significant increase in cases.
Health officials have distributed a standardized questionnaire to individuals who tested positive for Crypto to identify possible sources of exposure. The questionnaire covers topics such as food, travel, contact with animals, and water exposure, which is the most common route of transmission for Crypto. International travel and swimming (both in the UK and abroad) appear to be linked to the outbreak.
Out of 463 respondents who completed the questionnaire, 250 (54 percent) reported international travel. Among 215 individuals in England, 45 percent reported traveling to the Spanish mainland or the Balearic Islands. Of the 353 respondents who provided information about recent swimming activities, 234 (66 percent) confirmed that they had been swimming. While health officials noted a potential increase in swimming-related exposures compared to the same period last year, it is necessary to gather more data on the outbreak as well as general swimming and travel trends to establish firm connections.
Although the exact cause of the UK’s surge in Crypto cases remains unknown, we have a good understanding of how Crypto is generally transmitted. This microscopic parasite infects the human intestines and leads to watery diarrhea. After infection, hardy and thick-walled forms of the parasite (known as oocysts) are shed in feces. Parasite shedding begins with the onset of symptoms and can continue for weeks even after the symptoms have resolved. The parasite spreads through the fecal-oral route, which can occur through various routes of fecal contamination such as contaminated hands, surfaces, soil, food, and water, ultimately leading to ingestion.
Recreational waters, such as swimming pools, are the most common source of infection. Crypto oocysts are highly resistant to chlorine, allowing them to survive in properly chlorinated pool water for over a week. When an infected or recently ill individual enters a pool, the oocysts can contaminate the water. As the Centers for Disease Control and Prevention straightforwardly explains, germs can enter the water “from small amounts of poop rinsing off swimmers’ butts.”
An infected person can shed tens of millions of oocysts, but it only takes ingesting 10 or fewer to trigger an explosive infection. Health officials strongly advise individuals with diarrhea caused by Crypto to refrain from swimming and to wait at least 14 days after recovery before swimming again. While Crypto infections are generally not life-threatening for healthy individuals, they can be severe and even fatal for those with weakened immune systems. Common symptoms among healthy individuals include diarrhea, nausea, vomiting, abdominal pain, dehydration, weight loss, and fever. In the ongoing UK outbreak, more than half of the respondents who completed the questionnaire reported symptoms lasting over 10 days.
