Whooping cough

Whooping cough, scientifically known as pertussis, is a highly contagious bacterial disease. It is often called the "100-day cough" because the coughing fits can last for many weeks. This illness is caused by a bacterium called *Bordetella pertussis*.

It spreads easily through respiratory droplets when an infected person coughs or sneezes. While people of all ages can be affected, the disease is especially dangerous for infants. Because it can lead to severe breathing problems, it remains a major focus for global public health.

The biological mechanism of the disease begins when the bacteria are inhaled into the respiratory tract. Once inside, the bacteria use surface proteins like pertactin and filamentous hemagglutinin to adhere to the ciliated epithelium in the nasopharynx. This is the layer of cells in the upper throat that uses tiny hairs to clear mucus.

After attaching, the bacteria multiply and release several dangerous toxins. One specific substance, tracheal cytotoxin (TCT), kills the ciliated cells in the airway. This prevents the body from clearing away mucus and debris, which contributes to the characteristic cough. Another substance, the pertussis toxin, can cause lymphocytosis, which is an increase in white blood cells. This can lead to pulmonary hypertension, a serious condition that is a major cause of death in pertussis cases.

The illness typically progresses through three distinct clinical stages. The first is the catarrhal stage, which feels like a common cold with a runny nose and mild fever. After one or two weeks, the patient enters the paroxysmal stage. This stage is defined by uncontrollable, violent coughing fits. About 50% of people in this stage will make a high-pitched "whoop" sound when they try to inhale after a fit.

The final stage is the convalescent stage, where the coughing fits gradually decrease. This stage usually lasts between one and four weeks, though coughs can return during future respiratory infections.

Medical history shows how much our understanding of pertussis has changed. Outbreaks of the disease were first described as far back as the 16th century. However, the specific bacterium responsible for the illness was not discovered until 1906.

A major turning point occurred in the 1940s when the pertussis vaccine became available. This development transformed how society manages the disease. In 2002 alone, the vaccine was estimated to have saved half a million lives. Despite these advances, the disease has seen a resurgence in the 21st century due to waning immunity and bacterial mutations.

The impact of pertussis is significant on a global scale. In 2015, an estimated 16.3 million people worldwide were infected. While the number of deaths has dropped significantly from 138,000 in 1990 to 58,700 in 2015, the disease remains a threat.

For the most vulnerable, the risks are much higher. Approximately 50% of infected children under one year old require hospitalization. Furthermore, nearly 0.5%, or 1 in 200, of these young children die from the infection.

Doctors use several methods to diagnose the infection and provide treatment. They can collect a sample from the back of the nose and throat to test for the bacteria. This is often done through a culture or a polymerase chain reaction (PCR) test.

If caught early, antibiotics like azithromycin, erythromycin, or clarithromycin can be very effective. These medicines work best if started within three weeks of the first symptoms. For pregnant women and infants under one year old, doctors recommend starting antibiotics within six weeks of symptom onset. Antibiotics help by decreasing the time a person remains infectious, which prevents further spread.

Prevention through vaccination is the most effective way to control the spread of pertussis. The multi-component acellular pertussis vaccine is between 71% and 85% effective.

Because protection from the vaccine decreases over time, additional doses are often needed for older children and adults. Vaccination during pregnancy is also highly recommended because it protects infants during their most vulnerable early months. Even though vaccinated individuals may have much milder symptoms, they can still act as reservoirs and spread the bacteria to others. This makes widespread immunization essential for protecting the entire community.