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Whooping cough — known medically as pertussis — is a highly contagious respiratory tract infection. Although it initially resembles an ordinary cold, whooping cough may eventually turn more serious, particularly in infants. In the more advanced stages, it's marked by the symptom that gives the disease its name: a severe, hacking cough followed by a high-pitched intake of breath that sounds like "whoop."

In the first half of the 20th century, whooping cough was a leading cause of childhood illness and death in the United States. But after the introduction of a vaccine in the 1940s, the number of cases gradually declined, reaching a low in the 1980s.

Since then, however, the incidence of whooping cough has been increasing, primarily among children too young to have completed the full course of vaccinations and teenagers whose immunity has faded.

With proper care, most teenagers and adults recover from whooping cough without complications. Whooping cough is more serious in children, especially infants younger than 6 months of age.

Once you become infected with the bacterium that causes whooping cough, it takes a few days to a few weeks for signs and symptoms to appear. When they do, they're usually mild at first and resemble those of a common cold, such as:

• A runny nose
• Nasal congestion
• Sneezing
• Red, watery eyes
• A mild fever
• Dry cough
• General feeling of being unwell and loss of appetite

After a week or two, signs and symptoms become worse and usually include:

• Severe coughing attacks that bring up thick phlegm.
• Coughing attacks — up to 15 coughs in a row — that end with a high-pitched whoop sound as you gasp for air. These may be so severe that your child vomits or turns red or blue from the effort.
• Fatigue from coughing so much.

In adults, signs and symptoms of whooping cough may resemble those of bronchitis, a respiratory infection that causes a nagging cough — you may have heard it referred to as the "100-day cough." Babies and infants with whooping cough may not whoop at all, or at least not as loudly as older children do. Some children with whooping cough may experience choking spells and turn blue in the face as they struggle to breathe after a coughing fit.

Severe coughing can result in tiny red spots caused by ruptures in blood vessels at the skin's surface (petechiae) in your upper body, as well as small areas of bleeding in the whites of your eyes. You may even bruise or break a rib if your coughing episodes are severe. Coughing may be worse at night.

Even after treatment to destroy the bacteria, your body continues to repair the damage to the lining of your trachea. As a result, the cough often lingers after the initial illness. With time, coughing usually lessens but can persist for six weeks or longer. Some people may even experience recurring episodes of coughing over the course of a year, especially when they contract a cold or other respiratory infection.

Whooping cough is an upper respiratory infection, which means it affects your upper airways, mostly the windpipe (trachea) and the tubes branching off from the windpipe (bronchi). It's 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's already infected. Whooping cough is most contagious early on, but the possibility of spreading the illness remains until the infection clears completely.

Once inside your airways, the bacteria multiply and produce toxins that interfere with your respiratory tract's ability to sweep away germs. Thick mucus develops deep inside your airways, causing uncontrollable coughing.

The bacteria also cause inflammation that narrows breathing tubes in your lungs. This narrowing leaves you gasping for air — sucking in air with a high-pitched "whoop" — after a fit of coughing.

Some people think of whooping cough as having gone the way of polio — a childhood disease eradicated thanks to a vaccination campaign. But whooping cough hasn't been wiped out. In fact, the number of reported cases in the United States has been increasing since a historic low of approximately 1,000 cases in 1976. In 2004, more than 25,000 cases were reported, the largest number since the 1950s, according to the American Academy of Pediatrics.

Whooping cough is thought to be on the rise for two main reasons. The whooping cough vaccine you receive as a child eventually wears off, leaving most teenagers and adults susceptible to the infection during an outbreak — and there continue to be regular outbreaks. In addition, children aren't fully immune to whooping cough until they've received at least three shots, leaving those 6 months and younger at greatest risk of contracting the infection.

Call your doctor immediately if you experience prolonged, severe coughing spells, especially if these spells make you turn red or blue, are followed by vomiting or occur together with a whooping sound when inhaling. Call your child's pediatrician if your child experiences any of the same symptoms.

In addition, call your doctor if you or your child has been exposed to someone with whooping cough, even if you've been vaccinated. You or your child may need treatment with antibiotics or perhaps a booster of whooping cough vaccine to prevent infection.

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

Sometimes, doctors diagnose whooping cough simply by listening to the cough. Medical tests may be needed to confirm the diagnosis. Such tests may include:

• A nose or throat culture and test. Your doctor takes 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.
• 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. This is a general test and not specific for whooping cough, however.
• A chest X-ray. Your doctor may want to use an X-ray to check for the presence of fluid in your lungs, which can occur when pneumonia complicates whooping cough and other respiratory infections.

If whooping cough is the diagnosis, your doctor will advise you to avoid contact with others during recovery because the condition is highly contagious. Don't return to work until your doctor approves. For the same reason, don't take your child with whooping cough to school or child care until your child's pediatrician gives the OK. In general, children should stay out of school while they are taking antibiotics for pertussis.

Your doctor will also notify health authorities who keep track of whooping cough outbreaks.

Teenagers and adults usually recover from whooping cough without complications. At worst, 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's not uncommon. But in infants — especially those under the age of 2 — complications from whooping cough are more severe and may include:

• Ear infections
• Pneumonia
• Slowed or stopped breathing
• Dehydration
• Seizures
• Brain damage

Because infants and toddlers are at greatest risk of complications from whooping cough, they're more likely to need treatment in a hospital. In infants under 6 months of age, complications can be life-threatening.

Treatment for whooping cough varies, depending on your age and the severity of signs and symptoms.

Older children, teens and adults
When whooping cough is diagnosed early in older children, teenagers and adults, doctors usually prescribe bed rest along with an antibiotic such as azithromycin or erythromycin. Although antibiotics won't cure whooping cough, they can shorten the duration of the illness and they shorten the period of communicability. If there is a confirmed diagnosis but a slow response to antibiotic therapy, it may be necessary to take the antibiotic for at least two weeks and maybe longer.

If the illness has progressed to the point of severe coughing spells, antibiotics aren't as effective but may still be used. Unfortunately, not much is available in the way of symptom relief. Over-the-counter cough medicines, for instance, have little effect on whooping cough. A case of whooping cough usually resolves in six weeks but may last longer.

Infants and toddlers
Almost all infants with whooping cough who are younger than 2 months, as well as many older babies, are admitted to the hospital to help decrease the risk of serious complications of the disease. Most babies treated for whooping cough overcome the condition without lasting effects, but the risk exists until the infection clears.

In the hospital, your child is likely to receive intravenous antibiotics to treat the infection and perhaps corticosteroid drugs, which help reduce lung inflammation. Sometimes a child's airway may also be suctioned to remove mucus that's blocking it. Your child's breathing will be carefully monitored in case extra oxygen is needed.

If your child can't keep down liquids or food, intravenous fluids may be necessary. In some cases, prescription sedatives will help your child rest. Your child will also be isolated from others to prevent the infection from spreading.

The best way to prevent whooping cough is with the pertussis vaccine, which doctors often give in combination with vaccines against two other serious diseases, diphtheria and tetanus. This three-in-one combination is known as the DTaP vaccine. It's a newer and safer version of the DTP vaccine, which is no longer used in the United States.

Doctors recommend beginning DTaP vaccination during infancy. The vaccine consists of a series of five shots, typically administered in the arm and given to children at these ages:

• 2 months
• 4 months
• 6 months
• 12 to 18 months
• 4 to 6 years

It takes at least three shots of the pertussis vaccine to fully protect a child against whooping cough, but a total of five shots are recommended by age 6.

Because immunity from the pertussis vaccine tends to wane by age 11, and because of the increase in cases of whooping cough in adolescents and teens between 11 and 18 years of age, doctors now recommend a booster shot for those in this age group — the tetanus, diphtheria and pertussis vaccine, or Tdap. (DTaP is the name of the pediatric vaccine; Tdap is the name of the booster for people 11 years of age and older.) The booster is given preferably at ages 11 or 12. This is in place of the traditional tetanus and diphtheria (Td) vaccine received at this age.

Recommendations for adults
The Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices also advises adults to receive a Tdap booster shot every 10 years instead of the Td booster shot. The Tdap vaccine helps protect adults from pertussis and reduces the risk of them transmitting the infection to infants. Adults who are or will be in close contact with infants under 12 months of age should also receive the vaccine.

Side effects of the vaccine may include fever, crankiness, vomiting or soreness at the site of the injection. These problems are more likely to occur after the fourth or fifth dose of the DTaP series than after earlier doses. After late doses, some children may develop swelling of the arm or leg in which the shot was given. Ask your doctor what you can do for your child to minimize or relieve these side effects.

In rare cases, severe side effects may occur, including:

• Serious allergic reactions, in which hives or a rash develop within minutes of the injection
• High fever (greater than 105 F)
• Seizures, shock or coma

Some people are concerned that the pertussis vaccine may cause neurologic impairment because some children developed brain damage after the immunizations. So far, however, researchers have not found a definitive link between the pertussis vaccine and brain damage. Still, research into this issue is ongoing. Children with known seizure or brain disorders may not be candidates for the DTaP vaccine.

Other vaccines
In 2002, the Food and Drug Administration approved another combination pertussis vaccine. In addition to helping protect against pertussis, diphtheria and tetanus, the vaccine, Pediarix, immunizes children against polio and hepatitis B, a serious liver infection. Because Pediarix protects against five diseases, children need fewer shots. But the vaccine also causes a wider range of side effects than does DTaP. Talk to your pediatrician about the best choice for your child.

Antibiotics
If a member of your household develops whooping cough, your doctor will likely prescribe antibiotics for the whole family to prevent spread of the infection to anyone else. And if you've had close contact with someone infected with whooping cough outside your family, you also may need to receive antibiotic treatment.

The following tips on dealing with coughing spells apply to anyone being treated for whooping cough at home:

• Get plenty of rest. A cool, quiet and dark bedroom may help you relax and rest better.
• Drink plenty of fluids. Water, juice and soups are good choices. In children, especially, watch for signs of dehydration, such as dry lips, crying without tears and infrequent urination.
• Eat smaller meals. To avoid vomiting after coughing, eat smaller, more frequent meals rather than large ones.
• Vaporize the room. Use a mist vaporizer to help soothe irritated lungs and to help loosen respiratory secretions. If you use a vaporizer, follow directions for keeping it clean. If you don't have a vaporizer, a hot shower or bath also can temporarily help clear the lungs and ease breathing.
• Clean the air. Keep your home free of irritants that can trigger coughing spells, such as tobacco smoke and fumes from fireplaces.

Whooping cough isn't necessarily something that can be overcome in a week or two. This bacterial infection may persist for six weeks or longer. That means you may need to be off work for an extended period while you recover from whooping cough yourself or attend to a sick child.

Be familiar with your company's sick-leave policy or short-term leave for such family health emergencies. As a parent, you may want to prepare a list of in-home child care providers whom you can call when your child has to be at home and you can't be there yourself.

As your child or teenager recovers from whooping cough, provide reassurance and comfort. Ask your child's pediatrician about specific measures you can take to ease your child's coughing spells and how you can protect other family members and caregivers from infection.