Today in Morbidity and Mortality Weekly Report authors published accounts of at least 27 cases of acute gastroenteritis (AGE) reported among hikers of the Pacific Crest Trail in August and September of 2022, suggesting a possible norovirus outbreak that sickened hikers who shared latrines and a cabin.

Though only 27 hikers responded to a REDCap survey posted on a Facebook group popular with Washington Pacific Crest Trail hikers in September of 2022 and reported illness, social media was littered with numerous accounts of AGE among Washington-based hikers throughout 2022.

Among survey responses from the 27 ill Pacific Crest Trail hikers, investigators collected symptoms, locations, and contact details. Twenty (74%) survey respondents reported an illness of short duration (median of 2.5 days), and 17 (22%) reported vomiting and diarrhea.

"Twenty-one (95%) survey respondents who reported an onset date noted that they became ill within a 73-mile stretch of the Washington Pacific Crest Trail; this suggested the potential for environmental exposure," the authors wrote.

A difficult environment for controlling norovirus

Environmental sampling of two latrines, a trail cabin, and water stations conducted in October showed no Escherichia Coli or norovirus contamination, but "…epidemiologic links all supported the conclusion that the outbreak was primarily caused by norovirus, and that exposure to contaminated surfaces within the cabin and VIP latrines likely amplified transmission.”

Hiking trails are a difficult environment to control for norovirus, the authors said, noting a lack of easily accessible clean water and soap for hand washing. Alcohol-based hand sanitizers, though common on camp sites, are not effective against norovirus.

• Global flu activity remains low, with a few parts of the world experiencing sustained or rising activity, the World Health Organization (WHO) said in its latest update, which covers roughly the first half of August. In South Asia, detections increased in Bangladesh, Bhutan, and Nepal. In South East Asia, flu remained elevated in countries including Malaysia, Singapore, and Thailand. In East Asia, Hong Kong's flu activity rose slightly above the epidemic threshold, mainly due to H3N2. In the Americas, flu activity remained above baseline in Costa Rica, El Salvador, Nicaragua, and Mexico. Of respiratory samples that tested positive for flu at national flu labs, 70.6% were influenza A, and of subtyped samples, 62% were H3N2.

   

  
• CSL Seqirus last week announced an award from the Biomedical Advanced Research and Development Authority (BARDA), part of the US Department of Health and Human Services (HHS), to deliver one bulk lot of H5N8 antigen to the US government as part of pandemic preparedness. The award is the third for Seqirus following ongoing outbreaks of highly pathogenic avian influenza. Earlier awards were for a H5N8 vaccine virus seed and a H5N8 vaccine candidate for a phase 2 study, which was produced at the company's facility in Holly Springs, North Carolina. H5N8 viruses belonging to the current 2.3.4.4b clade have caused outbreaks in poultry, with a few human cases reported from Russia in 2021.
• Four countries in Africa reported more polio cases this week, all involving vaccine-derived strains, according to the latest weekly update from the Global Polio Eradication Initiative (GPEI). The Democratic Republic of the Congo (DRC) reported one more infection involving circulating vaccine-derived poliovirus type 2 (cVDPV2), bringing its total for the year to 82. Kenya reported two more cVDPV2 cases, raising its total to five. Mali reported three cases involving the same type from three different regions, putting its total at six for the year. And Tanzania reported one case from Rukwa, its second of the year.