By Dr Themba Titus Sigudu

On any given day across African cities and towns, the air hums with the sound of street-food vendors calling out to customers, greeting neighbours, and sharing jokes over sizzling grills. This vibrant human interaction defines our food culture and sustains informal economies, but it may also carry hidden health risks. Emerging evidence shows that when food handlers speak, shout, or cough near uncovered food, microscopic saliva droplets may transmit harmful microorganisms.

Recent advances in mathematical and computational modelling now allow researchers to estimate how many droplets people emit while speaking and how far these droplets travel. The results are sobering: ordinary conversation at close range can release hundreds of droplets per sentence, and loud speech multiplies that number. In crowded or poorly ventilated food markets, these invisible emissions could settle on food surfaces or utensils, creating another route for contamination.

When speech becomes a vehicle for microbes

Public-health campaigns have long emphasised handwashing, temperature control, and safe storage. Far less attention has been paid to the air around food. Yet the same mechanisms that helped respiratory viruses spread during COVID-19, saliva droplets suspended in the air, also matter for food safety.

Mathematical models integrate fluid dynamics, droplet behaviour, and microbiological data to estimate how many viable bacteria and viruses might be carried in speech droplets. For example, Staphylococcus aureus, commonly found in the noses and throats of healthy individuals, has been repeatedly implicated in food-poisoning outbreaks linked to food handlers. Even brief speech over ready-to-eat food can deposit infectious doses on exposed items.

Laboratory and simulation studies show that speech produces droplets ranging from very fine mist-like particles to larger droplets visible under magnification. Smaller particles can remain suspended in the air for minutes, while larger ones fall onto nearby surfaces within seconds. Understanding this range helps identify risk zones, how close a vendor stands to food, how high a protective barrier should be, or how airflow affects where droplets land. Science is finally giving quantitative backing to what intuition long suggested: distance, barriers, and ventilation matter.

A Global South problem hiding in plain sight

The World Health Organization estimates that the African region experiences the highest per-capita burden of foodborne disease globally. Informal and small-scale food enterprises feed millions but operate in environments where sophisticated hygiene infrastructure is rare. Expecting every vendor to have stainless-steel counters or mechanical ventilation is unrealistic.

Real-world examples already show the consequences. In South Africa, recurrent outbreaks of staphylococcal food poisoning have been linked to improper food handling in informal and institutional settings. In Kenya and Ghana, studies of street-vended foods have detected high bacterial contamination levels even when food was freshly prepared, suggesting post-cooking contamination during handling and serving. Similarly, investigations in Nigeria’s urban markets have identified food handlers as key sources of microbial transfer, particularly where cooked food is displayed openly and vendors engage closely with customers.

These cases demonstrate that the risk is not theoretical. Speech-related contamination occurs in everyday African food environments, often without vendors or consumers realising it.

That is precisely why modelling is valuable: it provides low-cost evidence for practical solutions. By simulating local conditions, open stalls, tropical humidity, dust, and crowd movement, scientists can recommend affordable interventions such as transparent plastic shields, angled display tables, or repositioned fans that redirect airflow away from food.

From equations to everyday practice

Numbers alone will not change behaviour, but they can make the invisible visible. Simple visuals derived from modelling results can show, for example, that shouting substantially increases droplet release or that stepping one metre back can markedly reduce contamination risk. Such tools can be integrated into municipal food-safety training, turning abstract microbiology into clear cause-and-effect messages.

Vendors can be encouraged to:

• Turn their heads away while speaking over food
• Use transparent barriers that preserve customer interaction
• Keep cooked items covered when engaging with customers
• Position fans to move air upward rather than across food surfaces
• Each step is small, but together they can prevent thousands of avoidable illnesses.

The economics of prevention

Foodborne illnesses impose silent economic losses through healthcare costs, absenteeism, and market closures. The World Bank estimates global productivity losses from unsafe food at over US$100 billion annually, with the greatest burden falling on low- and middle-income countries. For informal vendors, a single outbreak can mean loss of income, damaged reputation, or forced closure.

By quantifying how everyday behaviour affects contamination, mathematical models strengthen the economic case for prevention. Modest investments in education, barriers, and market design are far cheaper than responding to outbreaks after they occur.

Building Southern scientific capacity

Most modelling studies originate in high-income countries under laboratory conditions that differ from tropical outdoor markets. The Global South must generate its own evidence. Local universities and public-health institutes can collaborate to measure droplet spread in real market environments, calibrate models to regional climates, and integrate microbial sampling.

Doing so would not only improve policy but also strengthen locally driven science. Instead of importing one-size-fits-all guidelines, African researchers can lead in designing context-specific food-safety solutions that respect livelihoods and culture.

Listening to science – literally

Speech connects people; it also moves particles. Recognising this dual role allows societies to design safer food systems without silencing the social fabric of markets. Mathematical modelling does not aim to restrict vendors’ voices, it helps them speak safely.

For the Global South, where informal food economies are lifelines, embracing such evidence-driven approaches is not a luxury. It is an essential step toward protecting both public health and economic dignity.

Dr Themba Titus Sigudu is a public health specialist and academic in the School of Public Health, University of the Witwatersrand. His expertise lies in epidemiology, food safety, and infectious disease surveillance, with a particular focus on foodborne disease risks, antimicrobial resistance, and the role of human behaviour in microbial exposure. His work emphasises evidence-based approaches to strengthening food safety systems and preventing infectious diseases in low- and middle-income country contexts, with the goal of informing policy and improving population health outcomes across the Global South.