Why a cough can persist long after an illness has been cured

When was the last time you walked into a public space and didn’t hear someone cough? After three years of shaking at the sound, it can be disarming to hear so many people coughing – and embarrassing if that’s you.

But take comfort in knowing that you are not alone. A persistent cough following an illness caused by a upper respiratory infection is surprisingly common. And unfortunately, with the rise of seasonal flu, COVID-19 and respiratory syncytial virus, or RVS cases in fall 2022 and winter 2023, there has been a lot of coughing lately.

Cough is a common symptom of these types of respiratory infections, and coughing is a complaint that results in an estimate 30 million office visits each year. Some 40% of them end up in a pulmonologist’s office like mine.

Given how ubiquitous persistent coughs are, you might assume the medical profession has a long list of treatments that we know work. Unfortunately, it depends on why you are coughing. But a cough from an upper respiratory infection usually goes away over time.

How does a cough work

Doctors have long wondered why cough duration varies so much following a viral or bacterial infection of the upper respiratory tract. The answer probably lies in the differences between people, such as the presence of a disease like asthma or chronic bronchitis. I see this same variability in my office: some patients develop a long-term cough, while others seem to cough much earlier, without a clear explanation.

The cough occurs due to a complex process which begins with an electrical impulse between nerves in the airways, including the nose and throat. There are two types of nerves that can trigger a cough in response to external stimuli: chemical receptors and mechanical ones called mechanoreceptors. Chemical receptors react to odors and fumes; they are the reason why people sometimes cough after inhaling spicy chili peppers sizzling in a hot skillet. Mechanoreceptors respond to sensations from irritants such as dust.

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When these nerves are activated, the throat closes and the pressure in the chest increases. This build up of pressure causes air and mucus to burst into the lungs at approximately 500 mph – a speed almost twice as fast like the fastest cars in the world.

Studies show that a viral infection changes the sensitivity of these same nerves. When you have a viral infection, the inflammatory process produces a molecule called bradykinin which causes the urge to cough. And we know that the virus itself can activate genetic changes which increase the sensitivity of these nerve pathways, leading to more coughing.

But when the acute phase of the infection is over and you start to feel better, the body repairs the damage caused by the inflammation of the airways and lungs. Thanks to this process, the cough reflex also decreases. And the molecular processes that made you cough and sneeze more frequently calm down and return to a normal state – at least in most cases. Unfortunately, in some people this process takes longer than in others.

Knowing how long is too long to cough

Doctors find it helpful to divide respiratory symptoms like cough into specific categories.

There is three main types of cough: acute, subacute and chronic. A sharp cough is what most people feel when they have an active viral infection. A subacute cough persists for three weeks or more after an upper respiratory illness. And a chronic cough is one that persists for more than 12 weeks. Chronic cough is most often caused by asthma, post-nasal secretions and, perhaps surprisingly to some, reflux.

Post-infectious cough is a variety of subacute cough and is the persistent cough that many people have after overcoming their respiratory infection. It can last for weeks or months and evolve into a chronic cough.

Because post-infectious cough is so common, doctors have long worked to determine how many people have a cough that persists after their other symptoms have disappeared. Those estimates vary between studies. A small study in Japan found that in people with subacute and chronic cough, 12% resulted from a respiratory tract infection.

When it comes to COVID-19, the best evidence to date shows that only 2.5% of people who contracted it also developed a chronic cough after infection. That number may seem small, but it translates to a lot of people coughing, given that the United States has more than 280,000 new cases of COVID-19 per week, as of early February 2023. The actual number, however, is unclear because studies that examine post-infectious cough are often small and only include people who have contracted COVID- 19 and showed up at their doctor’s office. or during a telehealth visit for evaluation.

No easy solution

THE American College of Thoracic Physicians and the European Respiratory Society published guidelines to help clinicians navigate these uncertainties and the lack of available data on the diagnosis and treatment of cough. Although the US guidelines were published in 2006, they still represent the best evidence available to clinicians and their patients.

About half of patients recover from their cough without any treatment. For those who do not, the limited data available suggests that inhalers, steroids, narcotics and certain over-the-counter medications may provide relief for some people.

In adults, evidence for the effectiveness of various treatments is mixed and limited. In my practice, I often prescribe a non-narcotic cough suppressant called benzonatate, sold as brand name Tessalon Pearls. It works by numbing the nerves in the lungs and airways, calming the cough reflex. Data on treatments in children are also lacking, and studies have shown that over-the-counter cough suppressants and antihistamines were no more effective than placebo.

Home remedies can also play an important role for some patients. Many people swear by honey, and there is limited evidence to support its benefits. A trial showed that honey was more effective for calm a cough than the placebo over a period of three days.

If in doubt, ask a doctor

Worrying about a persistent cough is understandable – a quick Google search can present many reasons for concern. Although this is not a very satisfying answer, most coughs eventually resolve on their own. However, if you are losing weight rapidly, coughing up blood, having night sweats, or coughing up a lot, you should tell your primary care provider. In rare cases, a subacute and chronic cough may be a sign of lung cancer or various forms of chronic lung disease.

If you’re just nervous about it and want more information and advice, that’s reason enough to see your doctor. After all, coughing is the reason for millions of office visits each year.

This article is republished from The conversation under Creative Commons license. Read it original article.