Infection: the facts and the fiction

Immunologist Dr Jenna Macciochi looks at some common myths surrounding immunity

It starts with a sniffle. Next thing you know, the whole household is sneezing, coughing and passing tissues. Before long, the common cold, or worse, the seasonal flu, is upon you all.With so much conflicting advice out there, it can be difficult to know what to believe. So let’s start by putting myths to rest with a simple guide.

No. 1 tip to avoid infection

In the mid-19th century, a Hungarian man called Dr Ignaz Semmelweis made an important discovery. He linked childbed fever among women who had just delivered their babies in the hospital to the failure of the doctors who delivered those babies to wash their hands after performing anatomical dissections of the dead. The key to reducing infection was simple: wash your hands. Semmelweis died before his theory gained support, but hand-washing remains a cornerstone of modern-day infection control.

Most people are infectious before they get symptoms

Before the onset of symptoms, a person may already have an infection. How this works depends on the germ in question. Respiratory viruses are best engineered to spread when you have physical symptoms; the more symptomatic you are, the more you sneeze and cough, the more likely you are to spread an infection. But sometimes you can infect others with a virus even when you are asymptomatic. For influenza, you are infectious one day before symptoms and five to seven days after their onset. Young children and patients with altered immune systems can spread the virus for longer periods of time.

It’s just a mild cold – am I less infectious?

Just because you have mild symptoms doesn’t mean the virus is mild. It may just mean that you lucked out with your compatibility genes for that particular germ and your immune system is able to control the infection. For this reason, it’s important to remember that even with minimal symptoms, you can still infect others and potentially make some people really sick, especially those who are vulnerable, including the elderly and very young.

Why do colds and flu strike in winter?

The flu season in the UK starts in October and is in full swing by December, generally reaching its peak in February and ending in March. For our Antipodean cousins, the season is flipped. Put simply, whenever and wherever there is winter, there is flu. A common misconception, however, is that flu is caused by cold temperatures. This is not quite true. Flu is caused by the influenza virus. Cold temperatures simply create conditions that make it easier for the virus to spread.

Scientists now know that the influenza virus is transmitted best at cooler temperatures and low humidity. So the viruses that cause the flu survive better in winter and are able to infect more people. Another reason is the lack of sunlight and the different lifestyles we lead in winter months: days are colder and shorter during the winter, so we spend more time indoors and are more likely to share air with someone who’s infected. Lack of sunlight leads to low levels of vitamin D, a key immune-nourishing nutrient. Having less vitamin D decreases our immunity’s ability to fight the virus.

You’ll catch a cold from being cold

‘Put on a jacket or you’ll catch a cold.’ I’m sure you were told this as a child, but nowadays it is usually dismissed as an age-old misconception. But it turns out that this advice contains a kernel of truth too. It has been shown that when you are exposed to the cold for a prolonged time you may not be able to launch the most robust immune attack. While this effect might be marginal in most healthy people, older people, young kids or those with underlying health issues may have an even harder time fighting off the virus. So, best heed your parents’ advice and bundle up when heading out in the cold! Wearing a scarf in winter does warm the air in the back of your throat, making it less hospitable for those seasonal viruses that prefer cool air.

Extracted from Immunity: The Science of Staying Well by Dr Jenna Macciochi (Thorsons, £14.99)

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