Background

Campylobacter species are gram-negative bacteria with different morphologies (from spiral to curved, or rod-shaped) [1]. They have single polar flagellum, bipolar flagella, or no flagellum, depending on the species. It has been reported that at least 12 species of Campylobacter cause human disease, the most common of which are Campylobacter jejuni and Campylobacter coli [2].

Many countries around the world recognize C. jejuni (~ 90%) and C. coli (~ 10%) as the major causative agents of human campylobacteriosis whose symptoms include diarrhea that occasionally is bloody, abdominal pain, and fever [3]. Rarely, serious long-term complications occur such as peripheral neuropathies, reactive arthritis, and Miller Fisher syndrome. Infection caused by C. jejuni is the most common reason of neurological sequelae [3]. Campylobacter is a zoonotic pathogen and its most common source is poultry [4]. In addition, contaminated water and food products, such as unpasteurized milk and contaminated fresh produce, are also known as other sources of Campylobacter infections [5]. Campylobacter infection can also occur from direct contact with infected animals, which usually carry the bacteria asymptomatically [4, 6].

According to recent data, there has been a rise in the global incidence of campylobacteriosis in most countries, although there is incomplete data from Asia, and the Middle East [7]. There is no comprehensive data on the prevalence of Campylobacter at the national level. This systematic review was conducted to provide comprehensive evidence on the prevalence of Campylobacter in human, animal, and food in Iran by using a systematic review and meta-analysis based method. Results of this study will serve as data that can be used for the prevention and control of Campylobacter infections in the country as well as guide to identify the research gaps.

Results

Overall a total of 536 articles were identified through PubMed, Scopus, and Web of Science, and 72 additional articles were identified through Google scholar, SID, and hand-based searching for the prevalence of Campylobacter species. Figure 1 illustrates the method applied for selecting eligible studies. 582 articles remained after removing duplicates. Based on the eligibility criteria, 457 articles were excluded. A further 5 full-text articles were excluded due to the following reasons Review (1), Case report (1), Abstract (1), confused text/incomprehensible data and duplicate data (1), Non-available full-text (1). Finally, 119 articles were included in the quantitative synthesis. Table 1 presents the detailed characteristics of every included study.

Fig. 1
figure 1

Diagram of identification and selection of studies for inclusion in the review

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Table 1 Characteristics of the included study
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Prevalence/proportion of Campylobacter spp. in meat/animal products and environment of Iran

An overview showing the pooled Campylobacter spp. prevalence data generated from Iranian meat (92 studies), environment (6 studies), fecal (79 studies) and animal product sample (44 studies) categories generated using the random effects model is provided in Fig. 2. The highest prevalence of Campylobacter spp. has been observed in white meat (43.9%) from 55 studies among the meat and animal products that was reported in different studies from 0 to 90%. Campylobacter spp. prevalence in white meat was higher for chicken (48.6%) than other types of poultry meat (33.9%). Within the red meat category by 37 studies, Campylobacter spp. was detected at an overall pooled prevalence of 7.9% (Table 2), which was reported from 0 to 24% in the literature. Campylobacter contamination in this category was mostly prevalent in buffalo (13.5%), followed by goat and sheep (8.6%), cattle (8.4%) and camel (2.5%) meat. While among animal products eggs were found to have a 5.5% prevalence of Campylobacter spp. contamination, with a high rate of contamination prevalence being observed for chicken eggs (9.9%) in eight studies compared to eggs of other types of poultry (4.2%) from 24 studies. The prevalence of Campylobacter spp. contamination detected among environmental samples was 14.9%. Vegetables were constituted environmental samples that showed highest prevalence (19.4%) of Campylobacter contamination. Water and sewage samples had prevalence of 15.4% and 7.4%, respectively. As the I2 heterogeneity index was more than 50, there was heterogeneity in the included studies.

Fig. 2
figure 2

Forest plot of pooled prevalence/proportion of Campylobacter spp. in white and red meat, product of animal, feces and environmental samples of Iran

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Table 2 Pooled prevalence/proportion of Campylobacter spp. in samples
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Prevalence/proportion of Campylobacter spp. in fecal samples

Literature review of 79 studies that investigated the fecal samples in animal [60] and human [34] revealed that pooled proportion of Campylobacter spp. was 18.7% in fecal samples. Among food animals, poultry had the highest contamination of fecal samples (46.8%). Domestic and wild animal had 21% and 14.1% contamination of Campylobacter spp. (Table 2). A proportion of 8.4% of human samples were positive regarding Campylobacter spp.

Prevalence/proportion of Campylobacter spp. by place of sampling

Table 3 presents an overview from the meta-analysis of Campylobacter spp. prevalence from Iran based on sampling places. Poultry feces (61.9%) and white meat (47.2%) were determined to have the highest Campylobacter spp. prevalence at the slaughterhouse. This was followed by white meat at market (42.6%) and farm (40%) levels. The lowest pooled prevalence of Campylobacter spp. was observed for milk sampled at farm (1%) and market (3.3%) levels, eggs sampled at market (5.4%) and red meat sampled at slaughterhouse (6.2%) levels. Campylobacter spp. prevalence in white and red meat, and milk samples at markets (sampled from retails, supermarkets and butcher’s) was higher than at farms (Table 3). Considerable proportions of wild animal (prevalence of 25.4%) and dog and cat feces (prevalence of 20.4%), were found to be contaminated with Campylobacter spp..

Table 3 Pooled Prevalence/proportion of Campylobacter spp. by sampling place
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Prevalence/proportion of C. jejuni and C. coli

As the C. jejuni and C. coli are the main causative agents of human campylobacteriosis, the pooled prevalence of these two species was determined in Iran samples. Most of the studies reported the prevalence of C. jejuni and C. coli in their samples. C. jejuni had higher pooled prevalence/proportion than C. coli in all of the obtained samples except for those derived from vegetables. Sewage (100%) (one study), milk (86.6%) (7 studies), human feces (83.3%) (33 studies) and water (82.8%) (3 studies) samples had the most frequent contaminations with C. jejuni (Fig. 3). Pooled C. jejuni prevalence in white meat (54 studies), egg (28 studies), poultry feces (19 studies) and red meat (35 studies) was 68.7%, 65.5%, 65.2% and 62.7%, respectively. Vegetable (2 studies) samples had the least pooled prevalence of C. jejuni (28%). On the other hand the highest pooled prevalence of C. coli was reported in vegetable samples (72%) followed by egg (33%) and red meat (24.1%) samples. Pooled prevalence of C. coli was zero (95%CI: 0–84.2%) in sewage samples (Fig. 3).

Fig. 3
figure 3

Pooled prevalence/proportion of C. jejuni and C. coli from literature in Iran based on the different categories. Error bars show the 95% confidence interval

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Pooled proportion of virulence genes in Campylobacter spp.

Despite the high number of studies that reported the prevalence of Campylobacter spp., a limited number of them investigated the virulence genes required for pathogenesis. CdtA, cdtB, cdtC, cadF and pldA had the highest number of investigated studies. Figure 4 shows the proportion of virulence genes in Campylobacter spp. cadF (97%) had the highest pooled prevalence in Campylobacter spp. in 28 studies, followed by racR (93.8%) (3 studies) and flaA (91.3%) (17 studies). VirB11 had the least prevalence (0%) in the Campylobacter spp. in 11 investigated studies. A total of 31% of Campylobacter spp. contained wlaN in 7 studies. With the sensitivity analysis, it was found that one of the studies pulls the results towards itself. The virB11 gene has the greatest impact on heterogeneity.

Fig. 4
figure 4

Pooled proportion of virulence genes in Campylobacter spp. isolates in Iran

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Discussion

Campylobacter spp. are regarded as the commonest cause of bacterial human gastroenteritis around the world [121]. In the present study, we tried to determine the prevalence of Campylobacter spp. in the food, animal and human samples of Iran based on systematic review of studies published from the country. Our findings showed that in Iran, white meat including, chicken and poultry accounts for the highest pooled prevalence of Campylobacter spp. These results are consistent with high average Campylobacter contamination prevalence that has also been observed for broiler chicken (36.7%) and turkey (11.0%) meat in Europe as reported by the European Food Safety Authority [122]. Campylobacter spp. (33.3%) represented the second most prevalent bacterial contamination of poultry meat based on a systematic review of European surveys [123]. As much as 48.6% of chicken and 23% of other poultry meat samples in Europe were contaminated with Campylobacter spp. [123]. Frequency of Campylobacter spp. contamination in chicken was reported as 99.5% in Italy, 93.7% in Northern Ireland, 84% in Ireland, 82% in Switzerland, 56% in Turkey, 53% in Spain, 51% in Austria, 50% in Poland, 14.9% in Sweden, and 9.7% in Romania [123]. In Portugal 40.3% of fresh broiler meat samples were reported to be contaminated with Campylobacter spp. [124]. Our analysis in this review shows that about 76% of broiler flocks in Shiraz, Iran were positive for Campylobacter. C. jejuni accounted for 22% whereas C. coli for 32% of the Campylobacter positive chicken samples [2]. The current study revealed a higher prevalence of C. jejuni than C. coli in white meat of Iran. Poultry carcasses had 35.37% and 19.82% prevalence of C. jejuni and C. coli contaminations, respectively from the slaughterhouses of Jahrom-Iran [20]. Campylobacter was recovered from 49.2% of poultry liver, 42.8% of gizzard 33.3% of heart and 25.4% of meat from poultry slaughterhouses at West Azerbaijan, Iran [30]. The quail meat had the highest contamination (68.4%) with Campylobacter spp. followed by chicken (56.1%), turkey (27.4%) and ostrich meat (11.7%). The high contamination of quail meat could be due to handling in slaughtering and packaging procedure that leads to higher cross–contamination [4]. The total prevalence of Campylobacter spp. in poultry meat sampled from Isfahan was 47.1% [4]. Meanwhile about 55.4% of hen carcasses sampled in processing plant of Ahvaz, Iran, were contaminated with Campylobacter spp. [38]. Turkey samples had contamination with Campylobacter spp. (62.1%) [39]. Duck samples were more contaminated (39.2%) than goose samples (26.1%) [74]. Hen liver had the highest frequency of Campylobacter spp. (63.6%), then was turkey (40%) and ostrich liver (16.7%) [88]. Liver was more contaminated with Campylobacter spp. than meat [104]. Recovery of Campylobacter was more in chicken (63%) than beef (10%) [110]. Sheep meat (3.10%) was the most contaminated in the meat samples followed by chicken (2.40%), beef (1.80%), and buffalo meat (1.10%) from Khuzestan. 81.30% of the isolates were C. jejuni and 18.70% were C. coli [26]. Campylobacter was detected in 49.5% of chicken and 8% of beef samples [28]. Lamb meat had the highest prevalence (12%) of Campylobacter spp. followed by goat (9.4%), beef (2.4%) and camel meat (0.9%) [36] in Isfahan and Yazd, which was according to the present study. Higher contamination of lamb and goat meat revealed the effect of manual skinning, evisceration and processing in abattoir and inadequate hygiene in transport, storage and cutting of meat in local butcheries. Lower rate of contamination of camel milk may be related to high number of homogenic bacteria in rumen of camel and H2 accumulation that leads to destroying of campylobacter [118].

In a study that examined individual unpasteurized bovine and ovine milk samples from Zanjan, Iran, Haghi et al. [15] detected no Campylobacter contamination, which was in contrast to most of other studies covered in the current meta-analysis and it could be due to that other studies examined bulk milk, but Haghi et al. investigated individual milk. Campylobacter spp. isolated from 2.5% to 12.5% of milk samples in Mazandaran, Isfahan and Mashhad. C. jejuni was detected in 2.5% to 13.88% of these milk samples [5, 54, 77, 79]. Results of the current study showed 5.5% detection of Campylobacter spp. in eggs. Another study showed 7% contamination of eggshell of hen, 5% of duck’s eggshell, 3.3% of goose, 2.5% of ostrich, 4.2% of partridge, 5% of quail and 3.8% of turkey’s eggshell to Campylobacter spp. [22]. Prevalence of C. jejuni (6.3%) was more than C. coli (1.3%) in avian eggs which was according to present study. Safaei et al. [41] observed no C. jejuni in table eggs. 18.67% to 31.6% of eggshell were contaminated with Campylobacter spp. [83, 101].

Examination of cecal contents of poultry conducted in Kurdistan revealed that 55% of samples were contaminated with Campylobacter spp. that included C. jejuni (86.2%) and C. coli (13.7%) [13]. Similar prevalence levels have also been reported in Iran based on literature reviewed here that found C. jejuni is more frequent than C. coli in poultry feces. Khoshbakht et al. [23] reported 67.8% of Campylobacter spp. in cattle and sheep fecal samples of Shiraz, which was higher than current study. C. jejuni and C. coli were seen in 78.5% of the samples simultaneously. Moreover, 2.9% and 12.6% of the samples were positive for C. coli and C. jejuni, respectively [23]. Prevalence studies conducted in Isfahan detected Campylobacter spp. in 10%, 8%, 5.3% and 4% of sheep, goat, cattle and camel feces [34]. Salari et al. (2020) observed no C. jejuni in Crested lark [42]. About 33% of pet bird feces were contaminated with Campylobacter spp. [61]. C. jejuni was detected in 48.62% of bird feces [27]. 52.3% of Persian fallow deer fecal samples which were collected from Dasht-e-Arzhan located in southwest of Iran, were contaminated with Campylobacter spp. [80], which was higher than the present study. Most of the studies reported higher prevalence of C. jejuni than C. coli in the foodstuffs [4, 26, 28, 30, 31, 35, 36, 38, 39, 44, 51, 55, 56, 60, 83, 85, 93, 99, 101, 104] and fecal samples [13, 61, 64, 65, 70, 74, 75].

Among environmental samples examined from northern Iran, the prevalence of Campylobacter spp. was higher in river water (36.92%) than fecal samples of poultry (34.88%), cow (28.57%), horse (20%) and sheep (9%) origin. The lowest contaminated environmental samples were those of sewage (7.4%) origin [66]. A study that have examined Caspian Sea’s water reported a Campylobacter spp. contamination prevalence of 2.66% [67]. In the investigation of vegetable samples, 15% of mushrooms in Shahrekord had Campylobacter spp. contamination [105]. Campylobacter spp. was detected in 3.5% of leafy vegetables marketed in Tehran [115]. These different reported rate of contamination could be due to the difference of geographical location and season of sampling, type and number of the samples, method of isolation, and different sanitary situation on farms and slaughterhouses [49, 74].

Our current study found that human diarrheal samples examined from Iran had a pooled Campylobacter spp. prevalence of 8.4%. Studies from central Iran reported that 33% of infectious diarrheal samples were positive for C. jejuni [8]. Among acute diarrhea samples examined in Tehran, Campylobacter spp. were detected in 8.6% of the samples of which 69.5% were C. jejuni and 24.5% was C. coli [16]. Jafari et al., [6] studied the prevalence of Campylobacter spp. in children under five years of age with acute diarrhea in Tehran. They found campylobacter in 5.5% of patients, equal to 10.8% of all isolated bacteria. In Shiraz ~ 9.6% of acute diarrhea samples were positive for C. jejuni [17]. 4% of fecal samples were contaminated with Campylobacter spp. [46]. 9.8% of diarrheic children was positive for C. jejuni [63]. C. jejuni was the major species recovered from human samples [122].

Pathogenesis of Campylobacter was associated with some virulence genes. cadF, flaA, and ciaB genes are essential virulence factors for adhesion and colonization of Campylobacter to epithelial cells in human intestine [68]. Some studies observed 100% prevalence of cadF virulence gene in C. jejuni [14, 24, 62, 68, 76] and C. coli isolates [24, 68] which was agreed with the current study. The CDT toxin leads to cell cycle arrest and promotes DNA damage; so, its presence is related with the severity of the campylobacteriosis [68]. Prevalence of cdtA, cdtB, cdtC, pldA, and iamA genes were 97%, 97%, 96%, 72%, and 60%, respectively in the isolates [14], which was higher than the current study. Prevalence of cdtA, cdtB, cdtC, racR and pldA was observed 100% in some studies [24, 25, 62, 68, 69, 76]. VirB11 gene was not detected in any of the strains [5, 24] that was according to present study and could be related to the plasmid nature of this gene [5]. Guillain–Barre’ and Miller-Fischer syndromes are associated with wlaN, cgtB genes and waaC gene [125]. Prevalence of other genes including iamA, and wlaN, was reported as 81.11%, and 82.22%, respectively [24], which was higher than current meta-analysis. Frequency of cgtB genes was observed as 22.22% [24] that was lower than present study. Frequency of ciaB was reported in 76.92% of poultry, 55.56% of cow and 100% of sheep fecal samples [25]. pldA and cgtB were detected in raw chicken Campylobacter isolates in Shiraz as 65.4% and 15.4%, respectively [62]. Prevalence of dnaJ was from 11 to 100% in different samples [69]. WaaC was detected in 100% of food isolates of C. jejuni and 75.6% of C. coli [5]. Campylobacter food isolates carried most of the virulence genes essential for pathogenesis that shows the high risk of these isolates for human.

Prevalence of Campylobacter spp. contamination was higher at market than farm level in Iran as determined in the present study, which is similar to observations from previous studies conducted in other countries [123]. Gonçalves-Tenório et al. [123] reported higher prevalence of Campylobacter spp. (44.3%) contamination at retail level than at the end-processing (30.7%) stage in poultry meat. Campylobacter spp. are able to colonize and attach to tissues of poultry during processing [126]. Carcass processing in the slaughterhouse including, scalding, washing and cooling was found not to decrease the level of Campylobacter spp. contamination of poultry meat [127]. Freezing significantly decreased chicken contamination with Campylobacter spp. during processing of poultry carcasses from 80 to 30% [73]. Washing reduced the contamination of sheep carcass from 10% after hiding to 8% after washing [106]. Since farms are considered as the initial site of contamination with Campylobacter, most preventive strategies must therefore be implemented at farm level by increasing of biosecurity and enhancing monitoring [128]. The higher contamination observed at market level may be due to uncontrolled temperature during transport of meat [5].

Poultry are regarded as a major source of this organism due to their carriage of Campylobacter spp. in the intestinal tract [127]. Similarly we also found here that poultry samples in Iran including meat and feces are associated with higher Campylobacter spp. contamination. The handling and preparation of broiler meat led to cross-contamination of poultry meat and is considered as contributing cause for one-third of human campylobacter infection in Europe while the remaining cases are related to the self-contamination of chicken with Campylobacter as the reservoir of the organism [122]. Establishing if such a link also exists in Iran is rather difficult due to the fact that there is currently neither notification nor investigation of food vehicles of human campylobacteriosis.

Conclusion

In conclusion the current systematic review and meta-analysis of Campylobacter prevalence shows that chicken has great concern for Campylobacter carriage in Iran. This must be considered in preparation of undercooked poultry such as barbecue. Most of the isolated Campylobacter carried virulence associated genes that show their potential pathogenicity. Since our analysis showed that the gastrointestinal tract and slaughtering facilities are among the main sources of Campylobacter contamination for poultry meat in Iran, implementing preventive and corrective actions at several stages mainly at farm level is very vital. Implementing control strategies specifically for this pathogen will have a remarkable impact on its incidence and production of safer meat for consumers. Moreover, consumer education in hand hygiene, sanitation of surfaces prior to and after handling meat, separation of raw and cooked meat and checking the temperature of refrigerator is also needed to reduce contamination and infections with this pathogen.

Methods

Search strategy

A systematic search was performed in PubMed, Scopus, and Web of Science electronic databases in papers that were published from November of 2021 to the end of January 2022. The search keyword was “Campylobacter coli “ or “Campylobacter jejuni” combined with the following terms: “Food”, “Animal”, “Chicken”, “Poultry”, “Meat”, “Beef”, “Lamb”, “Fish”, “Milk”, “Dairy”, “Egg”, “Sheep”, “Goat”, “Avian”, “Cow”, “Cattle”, “Human”, “Feces”, “Diarrhea”, “Gastroenteritis “ and “Iran” (Supplementary file). Handmade search was performed in Google Scholar and scientific information database (SID). PRISMA guidelines were used to perform the systematic reviews.

Selection criteria and quality assessment

Selection of studies were performed by these inclusion criteria: research studies including original article either published or in press; studies with a cross-sectional design to detect Campylobacter on the samples based on culture or PCR; had a known sample size; and studies with available full-text. Title and abstracts of the searched papers were assessed to identify articles that matched with the inclusion criteria. In some circumstances full texts were evaluated. The exclusion criteria include articles that did not follow standard methods, duplicate articles and reports, studies with unclear or incomprehensible text and analysis, articles that did not report the exact sample size and number /percent of Campylobacter. Positive samples Reviews; letters or editorial articles without original data were also excluded. Quality assessment of the eligible studies were performed by Joanna Briggs Institute [129]. Articles which gained 6 score (from 10) were eligible for data extraction. When two reviewers (EA and TZ) were disagreed about an article, seek the opinion of third reviewer (PS). Duplicates articles were removed by help of Endnote reference manager and also some of them were found by manual check.

Data extraction

Data extraction forms were designed in Microsoft Excel. Articles that obtained more than 60% of quality score were eventually included in the analysis as they were meet 6 out of 10 criteria of Joanna Briggs checklist. Following information was collected from the included studies: the first author’s name, date of publication, study design, study location, number of samples, source of samples (animal, human and environment), sample group (meat, food product?, feces and environment) and type of samples (human, domestic animal, wild animal, poultry, white meat, red meat, milk, egg, water, sewage, vegetable), sample species (chicken, poultry white meat, cattle, goat, sheep, camel and other red meat, hen egg and poultry egg), place of sampling (hospital, pet clinic, slaughterhouse, farm, market and environment), diagnostic technique (Culture, PCR, culture and PCR), prevalence of Campylobacter spp., C. jejuni, C. coli, virulence factors and quality score.

Statistical analysis

In this study, the data analysis was done with STATA 14 software (STATA Corp., College Station, Texas) with metaprop command. A random effect model was applied to determine the pooled prevalence and 95% Confidence interval of Campylobacter spp.. A forest plot was used to calculate the pooled prevalence with 95% confidence intervals. Statistical heterogeneity among studies was evaluated by computing I2, Cochran’s Q. 25%, 50%, and 75% of I2 values are classified as low, medium, and high heterogeneity, respectively. A subgroup analysis, sensitivity analysis, and meta-regression were performed on the basis of publication year, and type of sampling to evaluate sources of heterogeneity.