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Friday, February 13, 2009

Whooping cough (pertussis)

Whooping cough (pertussis) is an acute, highly contagious respiratory infection that is caused by a bacterium. The first outbreaks of pertussis were described in the 16th century. The bacterium responsible for the infection, Bordetella pertussis, was not isolated until 1906. The incidence of pertussis has been steadily increasing since the 1980s. According to the U.S. Centers for Disease Control and Prevention (CDC), a total of 25,827 cases of pertussis were reported in 2004 in the U.S.

Can whooping cough be prevented with a vaccine?
Whooping cough commonly affects infants and young children but can be prevented by immunization with pertussis vaccine. Pertussis vaccine is most commonly given in combination with the vaccines for diphtheria and tetanus. (Pertussis is the "P" in the DTaP combination inoculation routinely given to children, and the "p" in the Tdap vaccine administered to adolescents and adults.) Since immunity from the pertussis vaccine wears off with time, many teenagers and adults get whooping cough.

What are the stages, symptoms, and signs of whooping cough?
*The first stage of whooping cough is known as the catarrhal stage. In the catarrhal stage, which typically lasts from one to two weeks, an infected person has symptoms characteristic of an upper respiratory infection, including runny nose, sneezing, low-grade fever, or a mild, occasional cough, similar to the common cold.
The cough gradually becomes more severe, and after one to two weeks, the second stage begins.
*It is during the second stage (the paroxysmal stage) that the diagnosis of whooping cough usually is suspected. The second stage is characterized by:

-Bursts (paroxysms) of coughing, or numerous rapid coughs, are apparently due to difficulty expelling thick mucus from the airways in the lungs. Bursts of coughing increase in frequency during the first one to two weeks, remain constant for two to three weeks, and then gradually begin to decrease in frequency.
-At the end of the bursts of rapid coughs, a long inspiratory effort (breathing in) is usually accompanied by a characteristic high-pitched "whoop."
-During an attack, the individual may become cyanotic (turn blue) from lack of oxygen.
-Children and young infants appear especially ill and distressed.
-Vomiting (referred to by doctors as posttussive vomiting) and exhaustion commonly follow the episodes of coughing.
-The person usually appears normal between episodes.
-Paroxysmal attacks occur more frequently at night, with an average of 15-24 attacks per 24 hours.
-The paroxysmal stage usually lasts from one to six weeks but may persist for up to 10 weeks.
-Infants under 6 months of age may not have the strength to have a whoop, but they do have paroxysms of coughing.
The third stage of whooping cough is the recovery or convalescent stage. In the convalescent stage, recovery is gradual. The cough becomes less paroxysmal and usually disappears over two to three weeks; however, paroxysms often recur with subsequent respiratory infections for many months.

How is whooping cough transmitted?
Whooping cough is highly contagious and is spread among people by direct contact with fluids from the nose or mouth of infected people. People contaminate their hands with respiratory secretions from an infected person and then touch their own mouth or nose. In addition, small bacteria-containing droplets enter the air during coughing or sneezing. People can become infected by breathing in these drops.

Can adults get whooping cough?

Although whooping cough is considered to be an illness of childhood, adults may also develop the disease. The illness usually is milder in adults than in children, but the duration of the paroxysmal cough is just as long as in children. The characteristic whoop that occurs after paroxysmal bouts of coughing is recognized in only 20%-40% of adults with whooping cough. Because immunity from the pertussis vaccine decreases over time but does not necessarily disappear, adults who do become infected may have retained a partial degree of immunity against the infection that results in a milder illness. Whooping cough in adults is more common than usually appreciated, accounting for up to 7% of adult illnesses that cause coughing each year. Infected adults are a reservoir (source) of infection for children.

How is whooping cough diagnosed?

When a patient has the typical symptoms of whooping cough, the diagnosis can be made from the clinical history. However, the disease and its symptoms, including its severity, can vary among affected individuals. In cases where the diagnosis is not certain or a doctor wants to confirm the diagnosis, laboratory tests can be carried out. Culture of the bacterium Bordetella pertussis from nasal secretions can establish the diagnosis. Another test that has been used to successfully identify the bacterium and diagnose pertussis is the polymerase chain reaction (PCR) test that can identify genetic material from the bacterium in nasal secretions,
How is whooping cough treated?

Antibiotics directed against Bordetella pertussis can be effective in reducing the severity of pertussis when administered early in the course of the disease. Antibiotic therapy can also help reduce the risk of transmission of the bacterium to other household members as well as to others who may come into contact with an infected person. Unfortunately, most people with pertussis are diagnosed later with the condition in the second (paroxysmal) stage of the disease. Treatment with antibiotics is recommended for anyone who has had the disease for less than 21 days. Azithromycin (Zithromax), clarithromycin (Biaxin), erythromycin, and trimethoprim/sulfamethoxazole are antibiotics which have been shown to be effective in treating whooping cough. It is unclear whether antibiotics have any benefit for people who have been ill with pertussis for longer periods, although antibiotic therapy is still often considered for this group. There is no proven effective treatment for the paroxysms of coughing that accompany pertussis.
Antibiotics are also routinely administered to people who have had close contact with an infected person, regardless of their vaccination status.

Complications of whooping cough (pertussis)

The most common complication and the cause of most pertussis-related deaths is secondary bacterial pneumonia. (Secondary bacterial pneumonia is bacterial pneumonia that follows another infection of the lung, be it viral or bacterial. Secondary pneumonia is caused by a different virus or bacterium than the original infection.) Young infants are at highest risk for whooping cough and also for pertussis-associated complications, including secondary pneumonia. Data from 2001-2003 indicate that secondary pneumonia occurred among 4.9% of all reported pertussis cases.

Pertussis can cause serious illness and even death in young children; 13 children died from the infection in 2003. From 2004-2005, 66 deaths due to whooping cough were reported to the CDC, and 56 of these were children under 3 months of age. Most of the pertussis-related deaths have occurred in children who have not been vaccinated or who are too young to have received the vaccine.
Other possible complications of pertussis include seizures, encephalopathy (abnormal function of the brain due to decreased oxygen delivery to the brain), reactive airway disease (asthma), dehydration, and malnutrition.

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