A Scoping Review of “Wet Markets” and Their Risks to Public Health

Search Strategy

This scoping review follows Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Review guidelines (PRISMA-Scr). ²⁰ We performed a scoping review rather than a systematic review due to the wide range of study designs and outcomes of interest, which made quality of evidence assessments difficult to conduct at this early stage of research. This follows the approach of similar studies on “wet markets” and wildlife trade.^18,19 Structured searches were conducted in March 2024. Preliminary searches on PubMed and Scopus databases tested various combinations of keywords “public health,” “health,” “wet market,” “traditional market,” “live bird market,” “animal market,” and “wildlife market.” We chose these various terms because “wet markets” have been considered to be associated with trade in wild and live animals. ²¹ Scientific research databases were the focus of this review rather than including gray area literature (eg, briefs, government publications, organizational guidelines) because this study was concerned with primary data rather than reviews or expert opinion.

We captured the highest number of articles relevant to the study of the wet market context and health when relying on “wet market” as a search term. Using “traditional market” and “wildlife market” did not yield studies that researched health in contexts identified as “wet markets.” Articles that had included some of these other preliminary terms were ultimately captured when using “wet market.” Based on the number of preliminary search hits and to increase our breadth of coverage, “health,” “wet market(s),” and “wildlife” were finally selected search terms for publication title and abstract across PubMed, Scopus, and Web of Science. Abstracts of papers were read by 1 author to confirm that the study focused on “wet market” contexts. The search term “health” was deliberately chosen in order to have the widest scope for this review to capture research on population health, public health, global health, nutrition, veterinary medicine, and food safety topics because of the interdisciplinary aspect of One Health research. We could not rely on MeSH terms because during preliminary searches we found no results with “wet market” used as a MeSH term.

Figure 1 illustrates a flow chart of the search process. ²² These structured searches in PubMed, Scopus, and Web of Science generated a total of 465 results. After removing duplicates based on the PubMed results initially found, the unique results included: PubMed (n=175), Scopus (n=74), Web of Science (n=84). Two additional articles were identified from combing other bibliographies. These 335 articles were then screened for eligibility following the criteria below. If meeting these criteria, the articles were read in their entirety to reconfirm that they were related to public health in “wet market” contexts. Each was read and reviewed independently by 2 authors and screened for final inclusion given this review’s criteria. Data charting effort was then divided equally between 2 authors and subsequently cross-validated (see Supplementary Data S1). A third author resolved all outstanding conflicts. Subsequently, 144 studies were included in the final review.

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Figure 1.

Flow chart of search process. ²²

In order to be included for final review, publications had to meet the following criteria: (1) present empirical findings, (2) present public health research related to the “wet market” context, (3) be published online between January 2001 and March 2024, (4) be written in English, and (5) have the full online article available. Studies published prior to 2001 were excluded because there were very few and preliminarily screening found them largely irrelevant. A total of 49 articles were removed during screening because they provided commentary or review only, many of them using “wet market” to describe the suspected origin of COVID-19 but did not present new evidence. Ten articles were excluded because they could not be located online, and 3 were manually removed from final review because upon reading the full article, these articles did not discuss health or wet markets. We did not place any restrictions on study sample size, design, or location for final inclusion. To be included, papers needed to have collected data regarding a risk to human health within the context of “wet markets.”

Data Charting

Two researchers charted the data, extracting relevant descriptive information in order to more comprehensively understand patterns of evidence gathered on “wet markets.” Data included names of study authors and their universities, country locations of the studies, types of pathogens studied. In addition, a summary of each study was written to highlight the methods used and key findings available (see Supplementary Data S2).

We found that these studies, in the context of “wet markets,” have assessed 3 broad areas of risk to public health, which we categorized as 3 different origins of that risk: (1) foodborne, (2) environmental, and (3) behavioral. Articles that measured pathogen presence in food samples and focused on food as the primary source of risk to health from wet markets were coded as “foodborne.” Articles that focused on the facilities and general sanitation of markets in affecting foodborne pathogen levels and the presence of live animals in wet markets were coded as “environment,” to refer to the environment of wet market spaces as posing a risk to human health. Lastly, those papers that presented findings related to the behavior of market vendors, including education, handling, butchering, and storing practices, or consumers’ food choices as being the key concern for health were coded as “behavior.”

Foodborne Risk

Most articles in the review focused on wet markets as supporting a variety of foodborne-related risks to health (n=111), specifically foodborne pathogens (n=102), including bacteria, parasites, viruses, and fungi. From wet markets, researchers extracted bacterial samples from species sold for routine consumption including poultry (n=62), seafood (n=20), pork (n=32), beef (n=10), snails (n=1), and frogs (n=1). Many studies focused on prevalence and antibiotic resistance of nontyphoidal Salmonella spp. (n=44), E coli (n=17), and Campylobacter spp. (n=14). Seven studies examined chemical pollutants in food, including microplastics sampled from sharks sold for consumption, ²³ agricultural insecticides, ²⁴ and formaldehyde ²⁵ found in various species of seafood.

Studies that compared pathogens between samples taken at both supermarkets or hypermarkets and wet markets (n=47) somewhat less often (n=21) demonstrated higher pathogen prevalence from wet market samples. One study comparing chicken samples between hypermarkets and wet markets in Malaysia reported significantly higher prevalence of Listeria monocytogenes in hypermarkets (25.7%) than in wet markets (14.3%), though bacterial load was not very high. ²⁶ In addition, in studies reviewed, all samples from supermarkets or hypermarkets contained some level of pathogens. One study demonstrated 75% prevalence of Salmonella spp. in supermarket samples, compared to 85% in wet market samples. ²⁷ Another demonstrated higher (85%) Campylobacter spp. prevalence in wet markets, but 70% prevalence from supermarket samples. ²⁸

In this review, 43 studies were found to have measured antimicrobial capabilities of bacteria extracted from food samples at wet markets. Most studies reported high levels of antimicrobial capabilities, ranging from 30% to 80% prevalence.^29-32 One study demonstrated higher prevalence of antimicrobial-resistant bacteria in supermarkets compared to wet markets, ³³ while another reported higher prevalence in wet market food samples. ³⁴

Environmental Risk

We identified 40 studies that we categorized as those related to the environmental conditions of food retailers that may encourage pathogen growth and transmission. Among these articles we identified 2 subcategories: health risk from marketplace facilities (eg, butchering surfaces, water and sanitation) and health risk from the presence of live animals found within the marketplace environment.

Behavioral Risk

The third category that emerged from our review includes studies that focus on the behavior of vendors and consumers in wet markets. The identified articles discussed the need to encourage better hygiene practices, often by way of education (n=13). Studies reviewed included surveys and interviews of vendors to elicit self-reporting of hygiene practices. A seroprevalence study of E coli in tomatoes in Nigeria coupled with interviews of farmers and retailers at markets found that 83% of retailers were not aware that tomato contamination could result in foodborne illness, and most farmers reported that chickens and cattle could access their tomato fields. ⁶² Siddiky et al ⁶³ conducted a survey with 290 chicken vendors in Dhaka and report that while most (about 70%) vendors had a satisfactory level of knowledge regarding basic food hygiene, nearly all (96.9%) did not sanitize butchering equipment. Less than 30% responded that they knew about zoonoses, antimicrobial resistance, and pathways of foodborne pathogen transmission. Additionally, study authors noted that 44.1% of vendors were illiterate and 39.7% had only received primary school education; none had received food safety training or official certifications.

Similar demographics were reflected in a study of 177 wet market vendors in rural Laos People’s Democratic Republic. Philavong et al ⁶⁴ reported that all except 3 of the vendors were women. In addition, vendors’ median years of education was 5. They found that 35 of the 177 vendors sold wildlife meat across the 3 wet markets surveyed. When asked about their own perceived health risk of selling bushmeat, 86% reported no risk to personal health, and researchers observed low usage of personal protective equipment including masks, gloves, aprons, and boots.

Four studies regarding vendors’ behavior focused on avian influenza and trade in live birds. Authors of these studies recommend modifying markets selling birds by constructing centralized butchering facilities and cold chain distribution ⁶⁵ and expanding disease surveillance, ⁶⁶ as consumers reported buying birds at markets instead of modern retail settings, even after experiencing avian influenza outbreaks. ⁶⁷ Researchers also found that genetic reassortment of viruses between domesticated birds from different farms does occur at marketplaces. ⁶⁸

“Wet Markets” as a Term and Space

In this review of public health literature, a few findings become clear. Popular media, ⁶⁹ political leaders, ⁷⁰ and international scientific debates ¹¹ are concerned about places referred to as “wet markets” hosting viruses of mammalian origins like SARS-CoV-2, suggesting a research agenda focused on the sources and initial spread of novel pathogens. The research we found mostly studied nonexotic, commonly consumed, already butchered animals and seafood, as well as fruits and vegetables. It focused primarily on bacterial and parasitic pathogens such as Campylobacter and Salmonella associated with the safety of well-known foods rather than identifying rare or emergent pathogens. The few studies that did examine live animals did not collect data on the geographic sources or trading networks of these animals, which is a common concern for tracing the spread of diseases. At this stage, it is unclear how this research would underpin efforts to change market regulation and practice with regards to viral pathogens of pandemic potential. Institutions concerned with global and emergent health risks, such as novel viral pathogens, should prioritize research and surveillance that identifies and measures those risks. Addressing well-known health risks associated with food safety is a valuable public health activity, but it does not always overlap with efforts to identify and respond to novel circulating health risks, and it is not clear that the concept “wet market” is useful in formulating a scientifically and administratively practical response to either set of risks.

Although a few studies we reviewed were conducted in Africa and the Americas, the term “wet market” seems to be predominantly used in research on Southern China and Southeast Asia, which others also have noted. ¹⁹ However, it is not clear that any of the policy issues discussed within this “wet markets” literature are, in fact, confined to Asia.

Some articles initially screened for this review relied on generalizations regarding Asian cultural preferences for the purchase of live animals. These notions have the tendency to presume that wild animals are mixing with humans and food on a large scale, and this contributes to the idea that food markets in Asia are a major global health risk.^12,71-73 However, from our research, we have seen that research on wet markets focuses largely on issues related to food security and food safety. We also found an empirical study that assumes, within the risk assessment, that wet markets have a trade in live animals, and, therefore, living within proximity to wet markets increases health risk to humans. ⁵⁹ This shows that this assumption about wet markets has entered the general lexicon with embedded assumptions about zoonotic disease risk. It is hard to avoid the conclusion that there is a fundamental mismatch between global interest in Asian “wet markets” and the scale of research and surveillance that has been dedicated to them thus far.

Two studies, identified in our search but ultimately excluded from our review, used the term “wet market” in the article title or abstract when surveying the selling of live or butchered wild animals. The study authors, however, did not measure pathogen prevalence in the market or research food-related topics, nor did they consistently use the word use the word “wet market” in their articles, instead switching to “wildlife market.”^74,75 This shows an inconsistent usage of this term, especially as some scientists dispute that wet markets support the wild animal trade. ⁵ The vast majority of studies collected for this review did not discuss the context of “wet markets” or study the markets as hubs for live animal trade networks; instead, they considered marketplaces as venues in which to conduct research on food.

Many researchers focused on the condition of “wet market” facilities, most notably insufficient sanitation, high humidity levels, and poor refrigeration. In particular, researchers found that wooden surfaces for butchering support ideal conditions for bacterial growth. Although some articles mentioned commensal species found in market spaces (eg, geckos, rodents, cats, roaches), they did not mention commensal bats. Additionally, we did not find any articles studying the sale of live, wild-caught animals in places where consumable goods were also sold. This is a notable finding because of the close association between the presence of bats, sale of wildlife, proximity to food, and term “wet market” in the predominant opinion and review discourse,^12,76 and the World Health Organization’s urging member countries to close “wet markets” based on the premise of live, wild-caught animals being present.^2,77 Most articles did not reflect on the context of the “wet market” as motivating the study, they simply drew their samples from these places; however, some did state that the purpose of their study on food contamination was to improve conditions for those who rely on “wet markets” for everyday food consumption. ⁷⁸ This is an important insight if decisionmakers are to enact evidence-based policy that could dramatically alter key food systems for populations.

Some researchers have argued that markets should be classified based on their risk to human health, relying on indicators including the selling of live wild animals, the selling of wild meat, and the size and scale of trade conducted in the markets. ¹⁸ However, the term “wet market” does not alone hold much empirical weight, and seems to be grounded more in ideas that come from historic racial tropes. ⁷⁹ For example, researchers found that the biosecurity narrative about “wet markets” has little salience nor impact on decisionmakers, specifically in countries that many scientists may consider as having “wet markets,” such as Kenya, Philippines, and Vietnam. ⁸⁰

Policy and Implementation Challenges

While much attention has been given to wildlife possibly sold at “wet markets” in Asia, for which, the empirics at this time are quite limited, ¹⁹ the United States imports the highest number of live, domestic and wild animals. ⁸¹ Globally, most of these imported animals are sourced from less wealthy countries and regions, especially Central America, Indonesia, and Thailand. Richer countries generate significant demand for wildlife capture and farming. ⁸² Researchers found that 78% of all wildlife imports into the United States were caught from the wild. ⁸³ Most of these live, wild animals are sold at pet stores, swap meets, flea markets, and through online networks in the United States, which may fall outside the regulations of various government agencies and are not consistently tested for diseases. ⁸¹ This wild animal trade and the role of large-scale livestock production, which have been shown to lead to zoonotic disease outbreaks, ⁸⁴ are left out of scientific research if policymakers and scholars continue to exclusively rely on the concept of “wet market.” More research is needed on the links between the drivers of the wild animal trade, the corresponding zoonotic disease risk, and the places where that risk arises.

From this scoping review, it is clear that there is a mismatch between the public health evidence on “wet markets” and high-level political narratives that often use this term to describe possible sites of wildlife trade. Other researchers have have also noted this “epistemic disparity” in our real understanding of the relationship between wildlife trade and places called “wet markets.”^19,80 Our review shows that research has been conducted on pathogenic risks to public health in markets, and this should be addressed as part of any effort to regulate. However, how these food retailers are defined by and engage with their respective governments, public health agencies, and international organizations with respect to governance remains unclear.^18,85 Our findings also suggest that authorities might be understandably wary of economically, socially, and politically costly efforts to close or heavily regulate a poorly defined category of markets before it is clear just which factors pose significant local or global health risk. ⁷⁶

Other literature reviews have already offered replacements for the concept of “wet markets,” and our findings suggest that this is a productive direction. Lin et al ¹⁸ have proposed a risk-based typology that policymakers may consider when assessing “wet markets” and their risks to human health. Their work relies in many instances on findings from expert opinion, however, and does not unpack the very term of “wet market,” which we aimed to do in our review. Cantlay et al ⁸⁶ have shown that wild meat sales and consumption are a health risk, and they do not reference the term “wet markets.” ⁸⁶ Brookes et al ¹⁹ have similarly examined the literature on wildlife markets and assessed the type and volume of wildlife sold at various types of markets (none referenced as “wet”) and have concluded that there remains much uncertainty with regards to types of markets, what they sell, and the various risks they pose to human health.

Limitations

We cannot draw strong conclusions about the relative safety or risk of “wet markets” to health because of the limited research that has been conducted in these contexts and the inherent definitional limitations of the term “wet market,” which we believe our review has demonstrated. Indeed, our scoping review highlights the need for more research on the operational scope and definition of what researchers empirically mean when they use “wet market,” “traditional market,” “informal market,” “bazaar,” “wildlife market,” and so on. “Wet market” alone does not capture the variety of food retailers found across the world, as many of these terms are specific to countries’ languages, cultures, and geographies. More urgently for public health practitioners, these various characterizations have empirical implications for how decisionmakers think about governing the human–animal interface. Terms which appear consistent may not be at all.

An additional limitation is that data from food and marketplace monitoring conducted by government agencies may not always be published, especially given the political sensitivity of legal and illegal wild animal farming and trade. These are necessary considerations for public health decisionmakers moving forward.