Pathogens turn up in one in six samples from traditional food markets, review finds

Traditional food markets — the wet markets, live-poultry markets and farmers' markets that supply much of the fresh food eaten in low- and middle-income countries — have been linked to disease emergence for years without anyone quantifying how often they actually harbour pathogens. A new systematic review puts a number on it.

Writing in The Lancet Global Health, researchers pooled data from 247 studies comprising 597 detection records across 41 countries in 16 regions, covering work published between 1 January 2000 and 31 October 2025 [s1]. The headline estimate: the global pooled prevalence of market-source pathogens in traditional markets was 15.32% (95% CI 13.96–16.80) — roughly one contaminated sample in six [s1].

What is being detected, and where

The pooled figure hides sharp differences by type of pathogen. Prevalence was 19.41% for bacteria, 8.40% for viruses and 27.05% for parasites — so parasites, not bacteria, were the most commonly detected class [s1].

Geography mattered too. Detection was highest in South-East Asia, at 23.09%, followed by South Asia at 15.52% and eastern sub-Saharan Africa at 14.54% [s1]. And within markets, the setting made a large difference: fish and seafood markets showed the highest pooled prevalence, at 37.87%, well above the global average [s1].

The most useful pattern in the paper is a gradient. By sample type, the highest estimates came from fish and seafood, raw meat and environmental samples, while cooked foods, fruit and vegetables, and samples taken from market workers themselves returned lower estimates [s1]. The authors read that as a flow of contamination from animal and environmental reservoirs towards ready-to-eat foods and people — which is precisely where interventions can be targeted [s1].

How the estimate was built

The review followed PRISMA 2020 reporting guidance and was registered with PROSPERO [s1]. The team searched major English- and Chinese-language databases for cross-sectional or baseline studies reporting detection of zoonotic or foodborne pathogens in traditional markets or related retail settings [s1]. Studies were excluded if they were not conducted in traditional markets, lacked extractable data, had fewer than 20 samples, reported intervention outcomes, drew on duplicate populations, or failed to report prevalence [s1]. Each usable finding was logged as a detection record — a unique combination of pathogen, sample type and market setting — and study quality was rated with the Joanna Briggs Institute tool for prevalence studies [s1].

Pooled prevalences came from random-effects meta-analysis of logit-transformed proportions, with heterogeneity assessed and meta-regression used to probe time trends and the influence of study quality [s1]. Two findings from that step are worth noting. There was no significant global linear trend over time — prevalence has not obviously fallen across a quarter-century of studies — and higher methodological quality was associated with lower reported prevalence, a hint that weaker studies may overstate contamination [s1]. Leave-one-out analyses suggested no single study drove the overall result [s1].

The One Health reading

The authors' framing is a One Health one: traditional markets are persistent global hotspots for zoonotic and foodborne pathogens, especially in low- and middle-income countries and in high-risk food chains, and the exposure gradient they map out marks the points where surveillance and control could do the most good [s1]. They call for harmonised, prospective, multi-pathogen studies rather than the patchwork of one-off surveys the field now rests on [s1].

That patchwork is the review's own main limitation. Pooling 247 studies of varying design and quality, conducted across two and a half decades and 41 countries, produces a wide-angle picture rather than a precise count, and the finding that better studies report less contamination should temper how the headline number is read [s1].

The stakes

The burden this speaks to is large. WHO estimates that 866 million people — almost one in nine worldwide — fall ill each year after eating contaminated food, and that 1.52 million die [s2]. Unsafe food costs an estimated US$ 310 billion a year in lost productivity and medical expenses, and children under five bear 29% of the health burden, with 143,000 deaths in 2021 [s2].

Markets are only one node in that system, and contamination detected on a stall is not the same as an infection in a person. But the review makes a case that has been asserted more often than measured: that the places where humans, live animals, wildlife and the environment meet at close quarters are, reliably and across regions, where the pathogens are. Where to look next, it argues, is no longer a guess.

The fish and seafood finding sharpens that point. At a pooled 37.87%, seafood markets more than doubled the global average, and raw meat and environmental samples clustered near the top alongside them [s1]. Those are the settings where cold chains break, water pools and surfaces go uncleaned — the practical targets a One Health surveillance system would prioritise first.

Sources

• Market-source pathogens in traditional food markets, 2000–25: a systematic review and meta-analysis — The Lancet Global Health, September 2026
• Food safety (fact sheet) — World Health Organization, 4 June 2026