A study published late last week in Nature Communications details the evolution and spread of a strain of extensively drug-resistant (XDR) Shigella.

Using genomic epidemiology, a team of researchers led by the United Kingdom Health Security Agency (UKHSA) analyzed a collection of more than 3,000 isolates from a strain of XDR Shigella sonnei that has caused shigellosis outbreaks in the United Kingdom and several other countries (Australia, Belgium, France, and the United States) since late 2021. The analysis revealed an internationally connected outbreak with a most recent common ancestor in 2018 that has been primarily associated with spread among men who have sex with men (MSM).

Although shigellosis is commonly associated with exposure to food or water that has been contaminated by human feces and is known to spread in settings with overcrowding and poor sanitation, oral and anal sex has become a major route of transmission, particularly among MSM.

While earlier versions of the S sonnei strain were resistant to the first-line (ciprofloxacin) and second-line (azithromycin) treatments recommended by the World Health Organization for treatment of shigellosis, the emergent XDR strain carries an additional resistance gene that confers resistance to ceftriaxone and a plasmid that can share the gene with other enteric bacteria. The study authors suggest the resistance to ceftriaxone is likely being driven by bystander resistance resulting from the use of ceftriaxone for treatment of gonorrhea.

"Treatment for ongoing high rates of gonorrhoea in the UK thus likely contributed to the acquisition of resistance to third-generation cephalosporins into this circulating ciprofloxacin resistant lineage of S. sonnei," they wrote. "It is also possible that plasmid fitness cost played a role in the emergence of this XDR strain."

The authors say active surveillance of microbiota among MSM receiving antibiotic treatments for sexually transmitted infections could potentially help mitigate the further development of XDR or pan–drug-resistant strains of Shigella. They also call for open international sharing of genomic surveillance data to help identify early indicators of antimicrobial resistance threats.

Three countries—Chad, the Democratic Republic of the Congo (DRC), and Mozambique—reported more polio cases last week, all involving vaccine-derived strains, the Global Polio Eradication Initiative (GPEI) said in its latest weekly update.

Chad reported a circulating vaccine-derived poliovirus type 2 (cVDPV2) case from Logone Occidental, bringing its 2023 total to five.

The DRC reported nine more cVDPV2 cases, eight included in its 2023 total and one added to its 2022 total. The cases were from six different provinces. Also, the country reported 12 cases involving circulating vaccine-derived poliovirus type 1 (cVDPV1), eight included in its 2023 total and four included in its 2022 total. The infections are from three provinces.

Also, Mozambique reported one cVDPV1 case from Zambezia, its first case involving the strain of 2023.

More details about Peru's polio investigation

In March, Peru reported a vaccine-derived poliovirus type 1 (VDPV1) case involving an unvaccinated child with no travel history whose paralysis symptoms began in December. In an Apr 7 update, the Pan American Health Organization (PAHO) posted an update on the investigation, which notes that health officials are waiting on test results for another suspected case as well as those for the first patient's asymptomatic contacts.

PAHO said a genetic analysis done at the Oswaldo Cruz institute suggests the virus isn't related to any other detected VDPV1 strains, signifying a new strain. Health officials are testing nine fecal samples, including that from a child younger than 18 months from Atahualpa native community who developed paralysis symptoms. The samples also include four contacts and four unvaccinated children as part of community surveillance.

The Centers for Disease Control and Prevention (CDC) said last week that its investigation into a Listeria outbreak linked to enoki mushrooms has ended.

The agency said in a food safety alert that the outbreak caused five illnesses in four states (California, Nevada, Michigan, and New Jersey), with five hospitalizations. Samples were collected from October 5, 2022, to February 4, 2023. Case patients ranged in age from less than 1 to 63 years.

Two of the case patients reported eating enoki mushrooms or eating at restaurants with menu items containing them. Of the three who did not report eating enoki mushrooms, two said they had shopped at grocery stores or eaten at restaurants that sell Asian foods.

The long, thin-stemmed mushrooms are popular in Japanese, Chinese, and Korean food and commonly used in soups and stir-fried dishes. They have now been linked to two multistate Listeria outbreaks and more than 20 recalls of enoki mushrooms because of potential Listeria contamination have been issued since 2020.

Whole-genome sequencing showed that bacteria from case patients were closely related genetically, suggesting people got sick from the same food. Investigation by the Food and Drug Administration (FDA) identified the outbreak strain in a sample of Utopia Foods-brand enoki mushrooms imported from China, which have subsequently been recalled.

Officials in Missouri and Maryland also found outbreak strains from samples produced by China's Shandon Youhe Biotechnology Co. The CDC and FDA are advising people not to eat enoki mushrooms produced by the company.

Listeriosis can cause a variety of symptoms, such as fever and diarrhea, and can be especially serious and even deadly in pregnant women, seniors, and those with weakened immune systems. The CDC says people who are pregnant, aged 65 or older, or have weakened immune systems should not eat raw enoki mushrooms and that restaurants should cook the mushrooms thoroughly before serving them.