Introduction

Non-typhoidal Salmonella (NTS) is a predominant etiological agent of foodborne disease globally, contributing substantially to public health challenges and economic losses [1]. Globally, NTS is responsible for 93.8 million cases of foodborne illness each year, with an estimated 94% of salmonellosis cases attributed to contaminated food [2]. Unlike typhoidal strains, which are primarily associated with systemic infections in humans, NTS encompasses a diverse group of Salmonella enterica serotypes that cause self-limiting gastroenteritis but can also lead to invasive disease, particularly in vulnerable populations [3].

The primary reservoirs for NTS are animals, and transmission to humans occurs mainly through consumption of raw or contaminated food of animal origin, such as poultry, beef, pork, eggs, and dairy products [2, 4]. However, person-to-person contact, contact with pets, rodents, and amphibians, and environmental exposures have been reported [5–7].

The diversity of NTS serotypes is remarkable, with S. Typhimurium and S. Enteritidis being among the most prevalent worldwide [8]. In Africa, S. Typhimurium is the predominant strain, commonly associated with beef and poultry, whereas S. Enteritidis is more frequently linked to chicken and egg products. Other serotypes, such as S. Infantis, S. Newport, S. Dublin, S. Heidelberg, and S. Weltevreden, contribute significantly to the global burden of NTS, each exhibiting unique geographic and food source associations [2]. There is a significant knowledge gap regarding the distribution of Salmonella serotypes in Ghana, primarily due to limitations in serotyping capabilities. Consequently, most studies only identify Salmonella isolates at the species level, leaving detailed strain information largely unexplored.

In Africa, the burden of NTS is disproportionately higher compared to other regions, reflecting challenges in food safety, surveillance, and public health infrastructure [9]. A systematic review and meta-analysis covering 27 African countries highlight the widespread prevalence of NTS in food animals and animal-derived products, particularly in poultry, cattle and pigs, which are major sources of protein in many African diets [10]. The intensification of commercial meat production in Africa, while offering economic benefits, also increases the risk of foodborne outbreaks if food safety practices are not adequately enforced.

NTS remains a significant but underreported food safety issue in Ghana. Salmonella serotypes have been isolated from a variety of food sources, including beef, raw cow milk, poultry, and vegetables [4, 11]. Studies have reported Salmonella prevalence rates ranging from 1% to as high as 73% in different food matrices, with the highest rates observed in ready-to-eat (RTE) salads and raw animal products [11]. However, the true burden of NTS in Ghana is likely underestimated due to limited surveillance systems and underreporting of foodborne disease outbreaks [4, 11]. A substantial proportion of Ghanaians obtain meat from local open-air markets, where butchers and vendors display fresh meat under ambient conditions. This practice often results in prolonged exposure of meat to environmental contaminants and microbial agents. These markets are often central to the local economy and a place where people can find various goods and services. Market-based surveillance of food products for Salmonella is ideal for the identification of potential sources of contamination and tracking the prevalence of different Salmonella serotypes.

Continuous integrated surveillance of Salmonella serotypes using a One Health approach between animals and environment is vital for risk assessment, outbreak identification, tracking regional trends, and formulating targeted interventions [12]. Collectively, this information enhances the effectiveness of food safety and public health strategies, thus contributing to a reduction in the incidence of Salmonella infections within affected communities in the country. The study sought to determine the prevalence and distribution of Salmonella serotypes in various animal-source food and products, RTE foods that contained animal products, as well as fecal samples from informal markets, farm environments and slaughter facilities within selected districts in Accra, Ghana to provide a baseline data on the Salmonella serotypes.

Materials and methods

Study sites

This study was conducted across nine selected markets, 11 livestock farms, and 2 slaughter facilities in six Metropolitan, Municipal and District assemblies (MMDAs) in the Greater Accra Region of Ghana, namely: Accra Metropolitan Assembly (AMA-Kaneshie and Agbogbloshie market), Ayawaso Central Municipal Assembly (Mallam Atta market), Weija/Gbawe Municipal Assembly (Gbawe slaughterhouse), La Nkwantanang Madina Municipal Assembly (LaNMMA), Shai-Osudoku (Asutsuare and Akuse markets), and Ningo-Prampram Districts (Tsopoli and Ningo Ahwiam market) (Figure 1). The Municipal Assemblies were chosen based on the popularity of the market, population density, and foodborne disease outbreak reports where these districts recorded a significant number of cholera and other diarrhoea cases [13].

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Figure 1. Map of the Greater Accra Region, indicating the selected markets, farms, and slaughter sites where samples were collected. Source of map: University of Ghana.

Results

Prevalence of Salmonella spp. in food and fecal samples

A total of 26 Salmonella spp. were isolated from the 696 samples, representing an overall prevalence of 3.7% (p = 0.0374). A significantly higher prevalence of 5.71% (25/438) was observed in animal-source food (p = 0.0026) compared to 0.4% (1/208) observed in fecal samples. Among samples that were positive for Salmonella, the highest prevalence was observed in fresh pork (73.1%, 19/26), followed by raw milk, “wagashie” and egg (7.7%, 2/26 each). Similarly, among the animal-source foods, fresh pork recorded the highest prevalence of 13.6%. No Salmonella sp. was isolated from RTE, beef, raw chicken, and chicken feces (Table 1).

Table 1. Salmonella spp. isolated from food and fecal samples.

Sample	Specimen type	Number of samples	Number of samples positive for Salmonella n (%)	p-value (within groups)
Food of animal origin	Raw cow milk	40	2 (5)	0.0026 (χ2 = 11.616)
	Wagashie (local cottage cheese)	36	2 (5.5)
	Eggs	185	2 (1.1)
	Pork	140	19 (13.6)
	Beef	16	0
	Chicken	21	0
RTE	Vegetable salad, grilled meat, rice meals, etc	50	0
Animal faeces	Chicken	70	0	0.0046 (χ2 = 6.650)
	Pig	138	1 (0.72)
Total		696	26 (3.7%)

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χ²: Chi square score; RTE: ready-to-eat.

Salmonella spp. were isolated from samples from four out of the six districts surveyed in this study. These districts included the LaNMMA, Accra Metropolitan Area, Weija/Gbawe (all more urban), and Shai Osudoku (more rural). The prevalence was 42.3% in Weija/Gbawe, 34.6% in the Accra Metropolitan Area, 15.4% in Shai Osudoku, and 7.7% in LaNMMA (Figure 2). Notably, no Salmonella were isolated from samples collected from the Ayawaso Central (highly urbanized) and Ningo-Prampram (rural district that is undergoing rapid urban expansion).

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Figure 2. Prevalence of Salmonella spp. in samples from the six districts in the Greater Accra Region. LaNMMA: La Nkwantanang Madina Municipal Assembly; AMA: Accra Metropolitan Area.

Diversity of NTS across districts

Isolates recovered from samples collected from the Weija/Gbawe district had the highest diversity of five out of the nine serotypes identified: S. Gaminara, S. Typhimurium, S. Hadar, S. Kaapstad, and S. Poona. This was followed by the Accra Metropolitan Area, where four serotypes were detected: S. Typhimurium, S. Virchow, S. Hadar, and S. Teddington (Figure 3). In contrast, samples from LaNMMA had the least diversity, with only one serotype, S. Enteritidis, identified. Of the six districts, these three have the highest population. Notably, S. Typhimurium was the most predominant serotype among isolates from Weija/Gbawe district, accounting for 66.7% of isolates in this district, which houses the largest abattoir exclusively for pigs, from where most of the pork samples were collected.

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Figure 3. Distribution of non-typhoidal Salmonella serotypes within the selected districts of the Greater Accra Region. LaNMMA: La Nkwantanang Madina Municipal Assembly; AMA: Accra Metropolitan Area.

Discussion

In sub-Saharan Africa, particularly in Ghana, NTS is the leading cause of gastroenteritis and invasive salmonellosis [17, 18]. This study provides important epidemiological insights into the prevalence, serotype diversity, and distribution of NTS in animal source food, RTE foods, and animal fecal samples from various districts within the Greater Accra Region of Ghana. By sampling both raw and RTE foods, the study offered a more comprehensive picture of Salmonella prevalence across the food chain. This approach aligns with One Health surveillance principles, which emphasize integrated monitoring across food, environment, and human exposure pathways.

This study found an overall Salmonella prevalence of 3.7%, with 5.71% in unprocessed animal source food and 0.4% in animal feces. Salmonella was not isolated from any of the RTE foods sampled. Previous studies in Africa have reported comparable Salmonella prevalence in animal source food, ranging from 4.0% in Nigeria [19], 5.5% in Ethiopia [20], 7.3% in Ghana [21], and 8.8% in North Africa [22]. However, other studies have reported a much higher prevalence, including 16–20% in Ethiopia [23] and 34.2% in Bangladesh [24]. For food borne pathogens like Salmonella, prevalence could be influenced by several factors including cross-contamination and poor hygiene during food processing and handling. This notwithstanding, the findings support the existing knowledge that animal-source foods are an important vehicle for transmission of foodborne pathogens [2]. Although raw animal products are the primary reservoirs of Salmonella, consumers are ultimately exposed through foods that are eaten without further cooking. Therefore, evaluating both raw and finished products provides a more complete understanding of the food safety risks along the value chain and helps determine whether contamination occurs before or after processing. This inclusion strengthens the public health relevance of the study by capturing the actual risk to consumers.

Salmonella is a prominent foodborne pathogen globally, often associated with poultry products [25, 26]. However, in this study, no Salmonella sp. was isolated from either chicken carcasses or chicken fecal samples, which is consistent with previous findings in Egypt [27] but contrary to an earlier study in Ghana, where a higher Salmonella prevalence of 61% in chicken carcasses [28] and 6% in the poultry environment was reported [6]. The variability in findings could be due to different methodologies employed, study locations, poor hygiene and biosecurity, and cross-contamination [29]. This study employed well-established methods for sampling fecal matter, involving the collection of fresh droppings and homogenization. Laboratory techniques included enrichment in BPW, selenite broth, and tetrathionate broth. XLD agar, which is sensitive for isolating Salmonella even in heavily contaminated samples with other Enterobacteria [30], was the culture media. All presumptively identified bacteria were confirmed with MALDI–ToF Biotyping. The absence of Salmonella in the fecal samples may also be attributable to low-level or intermittent shedding by the birds at the time of sample collection, resulting in bacterial loads below the detectable threshold [29].

Salmonella spp. was detected in 1.1% of eggshells of raw table eggs sampled from retail markets, mirroring a similar prevalence reported in Chile [31]. This finding differs from a previous study in Ghana, which reported a prevalence of 4.9% in eggshells [4]. In comparison, some studies have reported higher prevalence rates, such as 7.4% in South Korea [32], 15.6% in India [33], 14% in Nigeria [34], and 88.6% in Cameroon [35]. In the present study, it was observed that the footwear and equipment of farmers and attendants were disinfected before entry and upon exiting the cages and pens. This practice was to prevent the transmission of bacteria and other microorganisms between poultry housing units and the external environment. Although we did not assess the effectiveness of hygiene practices at the farm level, the low Salmonella prevalence reported in this study, could be attributable to this practice as well as the use of disinfectants during egg handling by the farmers, Despite the possibility of contamination of both the eggshell and the content, the current study assessed the prevalence of Salmonella spp., from only the eggshell because of the link between contamination of the eggshell and the risk of cross-contamination during consumer handling in the environment.

In this study, the prevalence of Salmonella spp., in pork was 13.6% which is lower than the 29.1% prevalence reported in Ethiopia [36], 37% in China [37], and 40% in Uganda [38], but higher than the 2.7% in Europe [39]. In contrast, countries like Sweden, Finland, and Norway, that adhere to strict EU trade standards, have reported much lower prevalence rates, often below 0.04% [40]. Pigs are asymptomatic carriers of NTS and can shed the bacteria in the farm and abattoir during processing of the carcass. Poor sanitation practices in animal husbandry, coupled with substandard hygiene conditions in abattoirs, may contribute significantly to the deterioration of carcass quality. This problem was common within the framework of our research.

It is important to note that the high prevalence of Salmonella spp. in pigs reported in the Weija/Gbawe district, as observed in this study, may be influenced by the sampling approach. Specifically, all pork and pig fecal samples were collected exclusively from the two largest slaughterhouses in the district, which supply pork to vendors and consumers throughout the region [41]. Due to cultural differences, particularly among Muslim communities, Christian denominations, and other tribes that do not consume pork, not all slaughterhouses in the study area process pigs, which may affect the representativeness of the sampling. In general, the four districts where Salmonella spp. were isolated represented a mix of urban and rural districts; hence, no association could be established.

Salmonella prevalence of 5% and 5.5% was observed in raw cow milk and locally produced soft cheese (wagashie), respectively. These findings are comparable to the 6% recorded in Ethiopia [20] and 6% in Ghana [21] but higher than the 1% in studies in New York, USA [42] and 0% in Ghana [43]. All cattle farmers in this study were observed milking their cows in the kraals, with fecal matter on the floor and sometimes on the udder prior to hand milking. The unclean milking environment and equipment, poor udder preparation, and hygiene of milk handlers observed in the study area could account for the higher prevalence. It is important to note that the Salmonella prevalence in the raw cottage cheese “wagashie” was lower than the 24% reported in an earlier study [21]. This study did not sample fried “wagashie”, which is usually how it is sold in the informal markets. However, Adzitey et al. [29], whose work compared the levels of Salmonella contamination in fried and raw wagashie, reported a significant reduction in the level of contamination in fried wagashie [21]. Thus, frying or cooking milk products and pasteurization of raw milk significantly reduced the level of or eliminated harmful pathogens.

Thermal processing methods such as frying, grilling, and smoking are highly effective in eliminating foodborne pathogens like Salmonella spp., thereby ensuring the microbiological safety of food products [44]. This effectiveness likely explains the absence of Salmonella spp., in all RTE food products examined in this study, consistent with previous findings reported in South Africa [45] and Iran [46]. In contrast, other studies from Ghana [47] and Colombia [48] documented higher Salmonella prevalence rates of 60% and 52%, respectively, in similar RTE food matrices. These higher contamination levels were attributed primarily to direct and indirect cross-contamination resulting from inadequate handling practices by food handlers. Per the national and international standards for food safety, Salmonella should not be present in any 25 g of food; however, 5.71%, representing 25 out of the 438 food samples from animal sources, were contaminated. The presence of Salmonella spp. in the food samples analyzed in the present study may present a public health concern and a food safety issue, especially when food is eaten raw or undercooked, or when there is cross-contamination. This suggests non-compliance with food safety standards and practices in the country.

S. Typhimurium and S. Enteritidis are reported to be the most frequently occurring Salmonella serotypes in food commodities and human samples in Africa [22, 21, 28, 49]. These serotypes have been associated with invasive NTS (iNTS) infections in children and immunocompromised adults in sub-Saharan Africa [17] and Europe, where they were also responsible for over 70% of reported human salmonellosis [50].

In this study, nine serotypes were identified, with S. Typhimurium (40.9%) being the most predominant. This aligns with findings from previous studies in Ghana and Europe [28, 51]. S. Typhimurium and Enteritidis are generalist pathogens, infecting a wide range of hosts, including humans, pigs, and poultry. Their broad host range stems from virulence genes on Salmonella pathogenicity islands (SPIs) and virulence plasmids, which enable bacterial invasion and immune evasion. Key SPIs, particularly SPI-1 and SPI-2, facilitate intracellular survival and enhance adaptability across species [52].

S. Enteritidis was detected only in egg samples, despite its generalist nature and ability to infect multiple hosts [22]. It is predominantly associated with poultry and eggs and is a major contributor to global outbreaks [53]. Archer et al. [4] identified five serotypes in table eggs from three regions in Ghana, mostly S. Chester and S. Hadar, with a few S. Enteritidis [4]. Our study, limited to only the Greater Accra Region, found lower serotype diversity in eggs (only S. Enteritidis), possibly reflecting regional variation. As a zoonotic strain, S. Enteritidis causes significant economic losses in animal husbandry and poses risks to public health and economic development [54].

The highest number of serotypes (7/9), S. Typhimurium, Kaapstad, Gaminara, Poona, Teddington, Virchow, and Hadar was found with pork samples. Yet this was far lower compared to studies in Malawi and Kenya, where 32 serotypes were identified in pigs and their environment [55]. Pigs can become asymptomatic carriers of the bacterium after infection and persist for up to 28 weeks in the tonsils and mesenteric lymph nodes until they are shed intermittently in their feces [56]. In the soil, they persist for up to 14 days, where they can infect piglets and handlers. In the present study, there was a higher prevalence of Salmonella in pigs’ than in the fecal samples. The low (0.4%) prevalence in fecal samples may reflect intermittent shedding or sampling limitations, as noted in a study [57].

The detection of Salmonella serotypes Poona, Germinara, and Teddington exclusively in pork samples is noteworthy, as these serotypes are generally regarded as environmental in origin and are more frequently implicated in the contamination of fresh produce, particularly fruits [53]. Their presence in pork may reflect indirect contamination routes rather than primary colonization in swine. Possible pathways include contact with contaminated water, soil, or surfaces during slaughter and processing, or cross-contamination from produce or feed ingredients within the production chain. The study found S. Virchow and S. Hadar only in pork, though these serotypes are typically linked to poultry outbreaks [53]. They have also been isolated from broiler farms and slaughterhouses in Ghana, Algeria, and Australia [7, 14]. It remains unclear whether contamination arose from pig lairage exposure or cross-contamination from poultry farms due to poor biosecurity.

S. Kaapstad, the most “unrestricted” serotype, was present in one pork sample, one raw wagashie, and one raw milk sample. Previous studies in Ghana have reported the isolation of this serotype from poultry, beef, and mutton [14, 58, 59]. This serotype was first isolated in 1973 from milk on a UK dairy farm, pig slaughterhouses, and consumers of unpasteurized milk from the farm [60]. It is known to cause mild gastroenteritis and invasive infections such as osteomyelitis in humans. There is limited data on its public health impact in Ghana, and it is not currently listed among globally recognized Salmonella serotypes of public health importance. However, its presence and diversity in foods of animal origin warrant a comprehensive investigation to inform surveillance purposes.

While we used a robust sample size, our study may be limited by selection bias inherent in a cross-sectional study design, warranting the need for a longitudinal study to fully capture trends in Salmonella prevalence across the seasons in Ghana. The sample size estimation was based on a 44% prevalence reported in an earlier study, which was derived from chicken and farm environment samples rather than the various animal-sourced foods that this study sampled from. While this represented the best available local estimate, it may not fully capture the true prevalence in the target population of this study. Nevertheless, the use of data from a different sampling frame introduces some uncertainty, and the findings should be interpreted within this context. Our study initially aimed to collect equal numbers of samples (20 per food category) across all sites. However, the final sample numbers reflect practical constraints and availability, rather than deliberate prioritization of food types. In several markets, meat products, especially beef and pork, were either unavailable at the time of sampling or vendors declined participation, limiting the number of meat samples we could obtain. Conversely, eggs were widely available, and vendors were generally more willing to participate, which allowed us to achieve a higher sample count in this category.

Insights into genetic diversity, risk factors, and transmission dynamics of Salmonella strains in food-producing animals were not explored in this study, but future studies could employ a molecular epidemiological approach using whole-genome sequencing.

The data collected between January 2020 and June 2022 provides a valuable baseline for understanding patterns of bacterial prevalence within the study period, particularly in settings where longitudinal surveillance is scarce.

This study provides critical insights into the prevalence and serotype diversity of NTS in animal source foods and selected RTE products in the Greater Accra Region of Ghana. The significantly higher contamination rates observed in raw pork, soft cheese (‘wagashie’), and raw milk underscore the potential risk these products pose to consumers. The predominance of S. Typhimurium, a serotype frequently implicated in human salmonellosis, reinforces the zoonotic and foodborne transmission potential of NTS in the region. Although fecal samples showed low prevalence, the detection of diverse serotypes in food products highlights the need for enhanced surveillance across the food production and distribution chain. These findings support the implementation of targeted food safety interventions, improved hygiene practices, and integrated One Health approaches to mitigate the burden of NTS infections in Ghana.