Diagnosing whooping cough in its early stages can be difficult to diagnose because the signs and symptoms resemble those of other common respiratory illnesses, such as a cold, the flu, or bronchitis.

If whooping cough is the diagnosis, the doctor will advise the individual to avoid contact with others during recovery because the condition is highly contagious. It is important not to return to work until a doctor approves. Children should not go to school or child care unless a doctor clears the child.

A doctor will also notify health authorities, including the U.S. Centers for Disease Control and Prevention(CDC), who keep track of whooping cough outbreaks.

Sometimes, doctors diagnose whooping cough simply by listening to the cough. Medical tests may be needed to confirm the diagnosis, including nose or throat cultures, blood tests, and a chest x-ray.

A nose or throat culture and test: A doctor will take a nose or throat swab or suction sample. The sample is then sent to a lab and cultured or otherwise tested for whooping cough bacteria (B. pertussis).

Blood tests: A blood sample may be drawn and sent to a lab to check for a high white blood cell count. White blood cells help the body fight infections, such as whooping cough. A high white cell count typically indicates the presence of infection or inflammation. However, this is a general test and not specific for whooping cough.

Chest X-ray: A doctor may want to use an X-ray to check for the presence of fluid in the lungs, which can occur when pneumonia complicates whooping cough and other respiratory infections.

The incubation period (the time between infection and the start of symptoms) for whooping cough is usually seven to 10 days, but can be as long as 21 days.

Symptoms of whooping cough typically last six to 10 weeks, but may last longer. Symptoms usually occur in three stages.

Stage 1: Stage 1 symptoms include cold-like symptoms, such as sneezing, runny nose, mild coughing, watery eyes, and sometimes a mild fever, lasts several days to two weeks. An infected person is most contagious during this stage.

Stage 2: During stage 2, cold-like symptoms fade, but the cough gets worse, changing from a dry, hacking cough to bursts of uncontrollable, often violent coughing. During a coughing episode, it may be temporarily impossible to take a breath because of the intensity and repetition of coughs. When finally able to breathe, the individual may take in a sudden gasp of air through airways narrowed by inflammation, and this sometimes causes a whooping noise. Vomiting and severe exhaustion often follow a coughing spell. But between coughing episodes, the infected person often appears normal. This is the most serious stage of whooping cough, usually lasting from two to four weeks or longer.

Stage 3: During stage 3, the individual may improve and gain strength, but the cough may become louder and sound worse. Coughing spells may occur sporadically for weeks to months and may flare up if a cold or other upper respiratory illness develops. This final stage may last longer in people who have never received the whooping cough vaccine.

Healthy adults who become infected with whooping cough often have a much milder form of the illness compared with children. But adults age 60 years and older are at increased risk of having severe symptoms and developing complications.

The severity of symptoms is, in part, influenced by whether a person was immunized against whooping cough and how long ago the immunization was given.

Respiratory complications can be severe in infants and may include suffocation, also known as asphyxiation. Seizures can occur in infants who have whooping cough. Middle ear infection, inflammation, called otitis media, may occur. A form of pneumonia is a potentially fatal complication in an infected person of any age. Emphysema (a progressive lung disease that results in shortness of breath and reduces the individual's capacity for physical activity), cerebral hemorrhage (bleeding in the brain), and encephalitis (swelling of the brain) can occur. These conditions may be serious.

Teenagers and adults (including older adults) usually recover from whooping cough without complications. Excessive coughing may cause a bruised or broken rib or a hernia (an abnormal protrusion of a loop of intestine through a weak area of abdominal muscle).

Children with whooping cough also may injure the muscles of the chest wall or develop a hernia that needs to be treated with surgery.

In infants, especially those under the age of two, complications from whooping cough are more severe and may include ear infections, pneumonia, slowed or stopped breathing, dehydration, seizures, and brain damage. Because infants and toddlers are at greatest risk of complications from whooping cough, they are more likely to need treatment in a hospital. In infants under six months of age, complications can be life-threatening. If an infant has a cough that has lasted for more than several days and has not gotten better, healthcare providers recommend seeing a doctor.

Whooping cough is an upper respiratory infection, which means it affects the upper airways, mostly the windpipe (trachea) and the tubes branching off from the windpipe (bronchi). Whooping cough is caused by the Bordetella pertussis bacterium, which is transmitted through droplets of respiratory secretions that are coughed or sneezed into the air by someone who is already infected. Whooping cough is most contagious early on, but the possibility of spreading the illness remains until the infection clears completely.

Once inside the airways, the bacteria multiply and produce toxins that interfere with the respiratory tract's ability to get rid of germs. Thick mucus develops deep inside the airways, causing uncontrollable coughing. The bacteria also cause inflammation that narrows the bronchial tubes in the lungs, leading to problems with breathing.

Whooping cough is thought to be on the rise in the United States for two main reasons. The whooping cough vaccine individuals receive as a child eventually wears off, leaving most teenagers and adults susceptible to the infection during an outbreak. Also, children are not fully immune to whooping cough until they have received at least three shots, leaving those six months and younger at greatest risk of contracting the infection.