The recent news that dozens of people in Ho Chi Minh City were hospitalized after eating banh mi did not come as a surprise to medical professionals like myself. What worries many of us is a familiar question that has never been fully answered: why do such incidents keep recurring despite years of warnings about food safety?

The answer may not lie in a single food stall or a single batch of contaminated ingredients. Instead, it may reflect a chain of everyday practices — from food preparation and storage to how vendors sell their products and how consumers choose their meals. As long as weak links remain in that chain, emergency rooms may continue to hear the same explanation from patients: "I ate a banh mi."

A loaf of banh mi with various kinds of fillings. Photo by Dang Phong

In Vietnam, banh mi has become a convenient breakfast option. In just a few minutes on the sidewalk, people can buy a hot, crispy loaf that is inexpensive, quick, and filling enough to start the day. Workers grab one before their shifts, students eat them before class, and office workers pick them up on their way to work. This convenience has made the sandwich a natural part of urban life.

Yet that same convenience can hide risks that many people overlook. A seemingly simple sandwich often combines numerous processed foods: cold cuts, sausage, pâté, roasted pork, raw vegetables, pickles, and various sauces. Each ingredient has its own storage requirements and safe shelf life. When these ingredients are prepared in advance and stored at room temperature for long periods, even one improperly stored item can affect the safety of the entire meal.

In preventive medicine, this is sometimes described as a "risk chain." Cooked food left out too long, utensils used interchangeably for raw and cooked items, vegetables that are not thoroughly washed, or food handlers touching multiple surfaces without proper hygiene — any single factor may seem minor. But together they create conditions in which bacteria can multiply rapidly.

Under such circumstances, a sandwich that was meant to be a quick and convenient meal can become the source of a food poisoning incident.

Previous cases have often shown that the problem lies not with the bread itself, but with the prepared ingredients inside it. Items such as pâté, roasted meat, sausage, or sauces can become favorable environments for bacterial growth if left unrefrigerated for extended periods. What makes this particularly concerning is that these changes are often invisible to customers.

For that reason, the safety of a sandwich depends not only on the vendor’s skill but also on how the ingredients are prepared, stored, and handled in the hours before they reach the customer. Even a small lapse in this process can turn a familiar food into a public health risk.

Many small food stalls operate in limited spaces where food preparation, storage, and sales take place in the same area. Street food has long been an essential and vibrant part of Vietnamese urban life. Step outside in the morning and it is easy to find bread carts, noodle stalls, pho shops, or sticky rice vendors along the streets.

However, the absence of refrigeration, the lack of separate spaces for raw and cooked foods, and inconsistent hygiene practices can increase the likelihood of contamination.

Authorities do conduct regular food safety inspections. But with the large number of small, independent vendors, maintaining consistent oversight remains a challenge. A stall may meet safety standards during one inspection, yet conditions may change soon afterward.

Food safety should not rely solely on penalties imposed after an incident occurs. Preventive measures are equally important. Helping small-scale vendors understand potential risks and learn practical ways to reduce them could significantly lower the chances of foodborne illness.

Regular training programs and clearer guidance on food storage, preparation, and hygiene practices could help reduce food safety risks while allowing street food culture to continue thriving.