Age-Stratified Patterns of Diagnostic Delay in Pertussis

Whooping cough, caused by a bacterium called Bordetella pertussis, is a respiratory infection known for its violent, uncontrollable coughing fits. In young children, the disease often follows a predictable pattern: it starts with mild cold-like symptoms, progresses to severe coughing spells that can make it hard to breathe, and eventually fades away. The bacteria are incredibly contagious, spreading easily through the air when an infected person coughs or sneezes. Because the infection is so dangerous for infants and so easily passed between people, doctors rely on catching it early. If treated quickly with antibiotics during the first few weeks of illness, the bacteria can be cleared from the body, and the patient stops spreading it to others. However, if the diagnosis is delayed, the infection can linger, allowing the bacteria to jump to family members, classmates, and neighbors, potentially causing outbreaks.

For decades, public health efforts focused heavily on protecting children through vaccination. Yet, in recent years, the disease has returned with force, even in places where vaccination rates are high. This resurgence has happened alongside the global COVID-19 pandemic, a time when people stayed home more and wore masks, which temporarily suppressed many respiratory viruses. As society opened up again, cases of whooping cough began to climb sharply. The question facing health officials is not just why the disease is coming back, but why it is taking so long to identify in certain groups of people. When a doctor sees a patient with a cough, they must decide whether to test for whooping cough immediately or wait and see if it is something else. This decision-making process, and the time it takes to reach a correct diagnosis, can determine whether an outbreak is contained or allowed to spread.

A team of researchers set out to understand exactly how long it takes to diagnose whooping cough and whether this time changes depending on the patient's age. They looked at the medical records of 787 people who had confirmed cases of the disease across two large health systems in South Carolina. The study covered a ten-year period, stretching from 2016 through early 2026, allowing the scientists to see how diagnosis patterns held up before, during, and after the peak of the COVID-19 pandemic. By examining the electronic health records, the team could trace every visit a patient made for respiratory issues leading up to the moment they were finally diagnosed. This approach let them measure the "diagnostic delay"—the number of days between a patient's first visit for a cough and the day a doctor confirmed whooping cough.

The results revealed a stark divide based on age. Children, particularly those between the ages of one and four, were diagnosed very quickly. In this group, about three out of four children received a confirmed diagnosis on the very first day they visited a doctor for their cough. In contrast, adults aged 50 and older faced a much longer wait. Only about half of these older adults were diagnosed on their first visit. For those who were not diagnosed immediately, the delay was significant. While children waited roughly one to two weeks on average before getting a confirmed diagnosis, adults over 50 waited nearly a month. The median delay for the oldest group was between 22 and 26 days. This means that for many older adults, they were sick and potentially contagious for weeks before the medical system identified the specific cause of their illness.

The researchers also looked at why these delays happened. They found that the symptoms older adults present are often different from the classic "whooping" cough seen in children. Instead of the dramatic coughing fits, older adults often report a persistent, nagging cough or shortness of breath that looks like a common bronchitis or a lingering cold. Because these symptoms are less specific, doctors are less likely to suspect whooping cough right away. The study showed that when older adults did visit the doctor before their final diagnosis, they were rarely tested for whooping cough using the most accurate early test, which looks for the genetic material of the bacteria. Instead, doctors in this group almost exclusively ordered blood tests that look for antibodies, the body's immune response to the infection. These blood tests take time to become positive; they often do not show up until weeks after the infection starts. By the time the blood test turns positive, the patient has already been sick for a long time, and the window for the most effective early treatment has passed.

In comparison, when children visited the doctor, they were much more likely to be tested immediately using the genetic test. This difference in testing strategy helps explain the gap in diagnosis times. The study found that the delay was not caused by insurance type, race, or the specific time period, such as whether the visit happened during the pandemic or after. The only factor that consistently predicted a long delay was the patient's age. Even when looking at the data from before the pandemic, the pattern held: older adults waited much longer for a diagnosis than young children. The researchers noted that this delay is not just a matter of inconvenience; it represents a missed opportunity to stop the spread. Because older adults are often in contact with grandchildren or other vulnerable people, a delay of several weeks allows the bacteria to circulate widely within a community before anyone realizes what is happening.

The study suggests that the way doctors think about whooping cough needs to shift. For a long time, the disease has been viewed primarily as a childhood illness, leading to a lower level of suspicion when an older adult walks into a clinic with a cough. The data indicates that this assumption is no longer safe. The resurgence of the disease is affecting adults just as much as children, and their symptoms are often subtle enough to be overlooked. The researchers point out that if doctors considered whooping cough earlier in the course of an adult's illness and used the genetic test sooner, rather than waiting for blood tests, the diagnosis could happen much faster. This would allow for earlier treatment and better protection for the people around them. The findings highlight a simple but critical reality: in the battle against a returning respiratory threat, the age of the patient can determine how quickly the medical system sees the danger, and for older adults, that system is currently moving too slowly.