Expert warns: persistent cough may signal bacterial infection; here's how to tell

A persistent cough that stretches into weeks or months has become a common complaint in the years since the pandemic, and doctors are now seeing patterns that break from what they once expected. July Torres González, a physician and epidemiologist trained at Universidad del Rosario with additional expertise in internal medicine and pulmonology from Universidad Javeriana, explains that the evolution of circulating viral variants has fundamentally altered how respiratory infections behave in the body.

Classically, a cough from influenza or a common viral infection would resolve within three weeks to a month. The body's immune system would mount a response, the infection would peak, symptoms would decline, and contagiousness would fade. But the viruses themselves have changed. Influenza mutates constantly through two primary mechanisms—antigenic drift and antigenic shift—allowing the virus to evade immune defenses. Cold weather and sudden climate swings amplify this risk, according to the World Health Organization and the U.S. Centers for Disease Control and Prevention. What has shifted since COVID-19 is the persistence. Torres now sees patients with coughs lasting two to three months, a duration that would have been unusual a few years ago. The new variants circulating in the population are producing symptoms that simply do not resolve on the old timeline.

To understand which viruses are actually in circulation, doctors rely on viral panels—molecular biology tests that identify the specific pathogen. These tests are typically reserved for patients sick enough to require intensive care, since testing everyone would be impractical. Through this surveillance, Torres notes that H1N1 continues to circulate periodically alongside newer variants. In Colombia, the National Health Institute reported 2,882 suspected cases of pertussis through mid-June 2025, of which 404 were confirmed, 1,963 were ruled out, and 515 remained under investigation.

The medical classification of cough duration has become more nuanced. An acute cough lasts fewer than two to four weeks—the typical duration of a normal flu. A subacute cough persists between four and eight weeks. Anything lasting longer than two months is now classified as chronic cough. Torres acknowledges that these definitions may shift again as new variants emerge, but for now they provide a framework for understanding what is normal and what warrants investigation.

When a viral infection damages the respiratory tract—from the nasal passages down through the bronchi—the tissue becomes inflamed and hypersensitive. The mucous membranes release inflammatory substances that alter both the quantity and quality of mucus production. This means that after the infection itself has cleared, the airway can overreact to irritants that previously caused no problem: sudden temperature changes, cold air, allergens, even office air conditioning. The cough persists not because the virus remains, but because the tissue has been sensitized.

Identifying a bacterial infection or bacterial pneumonia requires both clinical observation and imaging. On a chest X-ray, pneumonia becomes visible. Clinically, Torres looks for a drop in oxygen saturation, increased difficulty breathing, sweating, elevated heart rate, faster breathing rate, and fever. These signs together suggest that a secondary bacterial infection has taken hold and requires antibiotic treatment.

Prevention begins with practical measures: avoiding known triggers like abrupt climate shifts and allergen exposure, wearing masks to protect the airway, and washing hands frequently. But the foundation is nutrition. Torres emphasizes that protein and vegetables supply the micronutrients and microelements that the immune system needs to produce antibodies and activate defense cells. Meat, milk, eggs, and cheese are particularly important because they support vitamin D synthesis in the intestine, a process central to immune function.

For someone with a persistent cough, diagnostic testing can help identify the cause. A spirometry test measures lung function. A chest X-ray rules out pneumonia. For upper airway issues, a physical examination often suffices. For reflux-related cough, an endoscopy may be warranted. The goal is to move beyond guessing and toward a specific diagnosis that can guide treatment—whether that means waiting out a viral infection, treating a bacterial superinfection, or addressing an underlying condition like acid reflux that mimics a respiratory illness.