Shellfish tainted with hepatitis A virus make it past food-safety checks at times, causing outbreaks of serious illness. These can be better prevented by monitoring levels of the virus where the seafood is harvested, suggest Rosa Pintó and colleagues in the December issue of Applied and Environmental Microbiology.

 

The research team looked into two outbreaks linked to frozen clams imported to Spain from Peru. They found the virus in samples of seafood that were collected from patients but not importers of the food. In a separate analysis of data provided by the Peruvian Health Authorities, cases of the viral infection reported in the harvesting area were correlated with detections of the virus in clams.

 

“The correlation... points to the need to identify and prevent hazards that could cause food-borne illnesses, rather than relying on random sampling of finished products to ensure safety,” write the authors, from the University of Barcelona, Spain.

 

Jørgen Schlundt, Director of the Department of Food Safety and Zoonoses at the World Health Organization (WHO), agrees it is best to monitor water at harvesting sites, a strategy already advocated by WHO expert groups. “This would be in line with the thinking in other comparable areas, where we know that end-product testing is neither efficient nor timely.”

 

Viruses that infect the gastrointestinal tract are common contaminants in shellfish, and the most serious cases of viral infection are caused by hepatitis A. Some scientists suggest that lower levels of immunity to the virus in Europe could fuel a resurgence of the illness.

 

Nearly 300 people living in the city of Valencia were hit by outbreaks twice over 10 years, in 1999 and in 2008. Pintó and colleagues used reverse transcription PCR to look for genetic material belonging to the virus in samples of frozen clams collected from people who fell ill in both outbreaks. They also analysed seafood packages found in shops and provided by importers of the food in the more recent incident.

 

“HAV [hepatitis A virus] was detected in 44% of samples directly associated with cases but was undetectable in samples belonging to the same batches but randomly collected from the importers,” they write.

 

European Union regulations for seafood safety require that shellfish meat is tested for Escherichia coli, note the researchers. But they say studies have shown this is an unreliable marker of quality for the seafood. Other countries including the USA rely on monitoring at harvesting sites to ensure safety, but there is no international agreement on which method should be adopted.

 

This is the core of the problem, according to Schlundt. “Globalization of food trade means the food chain is not better than the weakest link in terms of food safety.” Improving safety systems will take developed and developing countries working together to build credible systems that will cover both export and domestic markets, he says.

 

Countries need to take action to minimise foodborne risks without overly restricting free trade. The World Trade Organization agreement on Sanitary and Phytosanitary measures sets out some “basic rules” on how governments can strike that balance. This agreement “actually calls for importing rich countries to help exporting poor countries achieve the relevant sanitary (health-protective) levels in relation to traded food,” Schlundt points out.

 

The difficulties in setting up policies to ensure food safety were evident this month in the USA, where Food and Drug Administration plans to ban the sale of raw oysters in warm months were scrapped as a result of strong opposition. Bacteria grow fast in warm conditions, causing the deaths associated with raw oysters seen in the country every year.

 

“More stringent requirements on the quality of growing waters are necessary,” says Schlundt. “Basically you should not grow shellfish in waters full of human (or animal) faeces.”

 

Both bacteria and viruses, but especially bacteria, flourish in water rich in this organic material. Keeping them in check to minimise health risks will also require collaboration between agencies that monitor food safety, environmental conditions, and sewage, according to Schlundt.