A recent study by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) reports higher incidence of Vibrio spp. in seafood as a result of seawater temperature increase. The presence of Vibrio spp. threatens consumer health, and has a direct financial impact on seafood manufacturers and healthcare agencies all over the world. As a result, many of these manufacturers have implemented High Pressure Processing (HPP) as a food safety measure against Vibrio spp., but without affecting the quality of seafood products.
Increased presence of Vibrio species in shellfish
The Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) published in early April 2020, a detailed study entitled “Risk assessment tools for Vibrio parahaemolyticus and Vibrio vulnificus associated with seafood”. The study reports an increase in foodborne disease outbreaks related to Vibrio species and mainly attributed to shellfish contaminated consumption.
The Vibrio species are gram-negative, halo-tolerant bacteria, capable of growing in cold marine environments and easily found in various types of seafood and fish. According to the report, Risk assessment of Vibrio parahaemolyticus in seafood, published by the FAO in 2011, V. vulnificus and V. parahaemolyticus (Fig. 1) are the most relevant Vibrio species in shellfish poisoning, due to their pathogenicity and prevalence.
Vibrio vulnificus can cause gastrointestinal disease, where symptoms appear quickly and might be fatal, especially in immunocompromised male patients, or those with chronic health problems such as liver disease, diabetes, or alcoholism. Fatal cases occur when the pathogen invades the bloodsteam, condition known as sepsis with 50-60% mortality rate. The microorganism has its natural habitat in coastal marine environments around the world and to date has been isolated from water, sediment, and a wide variety of seafood including fish, shrimp, oysters, clams, etc.
Vibrio parahaemolyticus is also widely distributed in marine environments, andit can be isolated from a wide variety of raw fish products, particularly seafood and especially oysters. It can produce TDH (Thermostable Direct Hemolysin), a toxin capable of serious gastroenteritis. The incidence of the disease in Asia, Europe and the United States diverges significantly.
Most Vibrio parahaemolyticus and Vibrio vulnificus outbreaks mostly occur in summer, when seawater temperature levels remain above 15 ° C (59 ° F). Due to the high prevalence of vibriosis and its seasonality, the United States Center for Disease Control and Prevention (CDC) voluntarily installed Cholera and Other Vibrio Illness Surveillance (COVIS) in 1989 and began monitoring sea water conditions to assess the risk of Vibrio spp. to track ongoing outbreaks.
After the implementation of this procedure and another series of measures, the National Outbreak Reporting System (NORS) reported a decrease of vibriosis incidences, reaching their peak in 1998, with 536 confirmed cases (Fig. 2). In 2004 and 2006, an exception occurred with 159 and 300 cases reported, respectively, which coincided with active hurricane seasons.
From the data collected by NORS, 67.4% of the cases of food vibriosis in the USA can be attributed to the consumption of oysters. As stated in our HPP Seafood: Shells Away with High Pressure Processing blog post, bivalves are fed by water filtration and this can lead to the accumulation of pathogens such as Vibrio spp.
The risk of contracting vibriosis is significantly lower in crabs, prawns and lobsters (4-10% of incidents) since, they are usually consumed cooked. However, cases of vibriosis continue to be reported, such and as we see in Table 1, with 22% of them being caused by these three products. In Japan, for instance, the consumption of contaminated boiled crab resulted in 691 cases between 1997 and 1998.
In Asia, Vibrio parahaemolyticus outbreaks are usually minor, with fewer than 10 cases but they occur frequently. In example, Japan reports between 500 and 800 outbreaks of V. parahaemolyticus annually, affecting about 10,000 people in the country. From 2006 to 2008, there were 2,682 reported cases of infection, with sashimi and sushi being the main culprits, representing 26% and 23% of the outbreaks, respectively.
There have also been significant outbreaks of V. parahaemolyticus in recent years in the Americas. Chile in particular, during 2004 and 2005, has recorded more than 10,000 cases of vibriosis related to mussel consumption. On the other hand, this infection is not common in Europe, although sporadic outbreaks have been documented in Spain and France (Table 2).
High pressure processing (HPP), an alternative to minimize the incidence of Vibrio spp. in seafood
In the United States, the Interstate Shellfish Sanitation Conference (ISSC) established ≥3.52 log10 reductions of Vibrio spp. as the shellfish processing standard, which is likely to be achieved by HPP at relatively mild pressure levels (150-350 MPa; Table 3). In example, processing at 293 MPa for 2 min met or exceeded 3.52 log10 reductions of V. parahaemolyticus inoculated in Pacific oysters (Ma & Su, 2011). These HPP conditions are also expected to comply with food safety regulations in other parts of the world, with government agencies allowing between 102-103 cfu/g counts of Vibrio parahemolyticus.
In addition to the enhanced safety, HPP has minimal effects on the sensory and nutritional properties of foods. HPP retains the natural appearance of bivalves (Fig. 3), infuses seawater to improve flavor, and facilitates shucking as also described in this blog entry. HPP minimizes the recontamination risk in cooked products as the meat is processed in its final packaging. Such is the case of our client in the US Seafarer’s Inc., where HPP allows to extend shelf life of freshly picked, cooked crabmeat from 7 to 21-30 days without the use of chemical preservatives.
Compared to other technologies, experts consulted by FAO, consider that HPP treatment applied to food provides an ideal balance to achieve the safety and high quality objectives demanded by the consumer, in addition to providing a series of interesting technical advantages for the producers of these foods, as summarized in Table 4.
With HPP, the pressure that is generated with cold water or at room temperature (4-25ºC / 40-75ºF), is transmitted instantaneously and uniformly on the product, regardless of its size or shape. As indicated in Table 3, 1 or 2 min of HPP treatment, may be sufficient to eliminate Vibrio spp., resulting in high yields (260-3,000 kg/h; 600-6,000 lb./h), with very low energy consumption. On the other hand, the pressure denatures the muscle that joins the shell to the meat of the shellfish, allowing a total recovery of the meat that considerably reduces labor costs.
Although it is true that rapid cooling, freezing or purification techniques keep the characteristics of the product “fresh”, it is also true that they are slow processes that increase the probability of survival of the microorganisms (Table 4). The same occurs in chemical preservation methods, which the survival of pathogens is more probable and it is necessary to consider consumer exposure to the additives used and the effect, sometimes undesirable, that they entail, such as this is the case of lipid oxidation produced by some strong oxidation agents. Additionally, irradiation offers conditions of quality and food safety very similar to those achieved by HPP. However, it is a treatment that is not well accepted by the consumer, being legally restricted in some countries. Finally, thermal processing is the only alternative capable of guaranteeing safe food, but the final quality of the product is negatively altered.