Pertussis (whooping cough)

While working in Ethiopia, I was stopped dead in my tracks by a stridorous breath taken by a young child. Having been a nurse for 10 years, it was a sound that I associated with severe respiratory distress. Having lived most of my life in a country with high immunization rates, I did not immediately recognize that sound as the "whoop" of pertussis.

Pertussis means "violent cough." It is also called "whooping cough" because of sound made when a breath is taken after a fit (paroxysm) of coughing – the sound I heard for the first time in Ethiopia. To the Chinese, pertussis is known as the "100-day cough."

Those terms describe pertussis well. People with pertussis can cough hard enough to break ribs, rupture the diaphragm, or rupture blood vessels in the eyes, the brain, or skin.

The term "whooping cough" can be a little misleading because not everyone with pertussis will whoop. Because our airway is larger than that of a child, adults with pertussis may not whoop at the end of a coughing fit. Babies are also less likely to whoop and more likely to gasp, gag, turn blue, or stop breathing than older children or adults.

Pertussis is caused by a bacteria called Bordetella pertussis (which is related to B. bronchiseptica, the cause of "kennel cough" in dogs), which is transmitted by respiratory droplets. The bacteria adhere to and kill the ciliated cells that normally move mucus and foreign material out of the respiratory tract. B. pertussis also produces toxins that inhibit normal immune responses to infection.

There are three stages to pertussis:

1. Catarrhal stage (also known as the prodromal stage) begins 7 to 10 days after becoming infected with B. pertussis (incubation period). The symptoms during this stage are similar to other upper respiratory infections and include runny nose, red eyes, watery eyes, low grade fever, and an occasional cough. This stage lasts about 1 to 2 weeks.

2. Paroxysmal stage takes its name from the paroxysms (fits) of violent coughing. The person will cough repeatedly in a single breath, which is followed by the characteristic "whoop." Vomiting after a fit of coughing is common. The paroxysmal stage usually lasts from 1 to 6 weeks, but can last longer.

3. Convalescent stage. Recovery from pertussis can take months. Coughing fits become less frequent and less severe, but can also recur during the convalescent stage. Unlike older children and adults, coughing fits may become louder and more severe in babies during this stage.

Unfortunately, immunity to pertussis, either through vaccination or though natural infection, wanes over time. For this reason, adults are a reservoir for B. pertussis. An adult who has been vaccinated against pertussis or who had pertussis as a child can have mild pertussis and, without realizing it, can infect infants who have not received enough doses diphtheria, tetanus, and acellular pertussis (DTaP) vaccine to be immune.

Complications of pertussis include pneumonia, encephalopathy, and seizures, all of which are more common in infants less one year of age. In the U.S., pertussis occurs most frequently in children less than one year of age, and most deaths occur in babies 3 months of age and under.

Babies are frequently infected with B. pertussis by household contacts – sisters, brothers, grandparents, fathers - and mothers.

Next, I'll discuss pertussis vaccines and recommendations.

References:

Long, S. S. & Edwards, K. M. (2009). Bordetella pertussis (pertussis) and other species. In S. S. Long (Ed.) Principles and practice of pediatric infectious diseases (3rd ed.). [Electronic version].

Paddock, C. D., Sanden, G. N., Cherry, J. D., Gal, A. A., Langston, C., Tatti, K. M. et al. (2008). Pathology and pathogenesis of fatal Bordetella pertussis infection in infants. Clinical Infectious Diseases, 47(3), 328-338. http://cid.oxfordjournals.org/content/47/3/328.long.

Slack, M. P. E. (2010). Gram-negative coccobacilli. In J. Cohen, S. M. Opal, & W. G. Powderly (Eds.) Infectious diseases (3rd ed.). [Electronic version].

Verma, A. (2008). Infections of the nervous system. In W. G. Bradley, R. B. Daroff, G. M. Fenichel, & J. Jankovic (Eds.) Neurology in clinical practice (5th ed.) [Electronic version].

Waters, V. & Halperin, S. (2009). Bordetella pertussis. In G. L. Mandell, J. E. Bennett, & R. Dolin (Eds.), Mandell, Douglas, and Bennett's principles and practice of infectious diseases (7th ed.). [Electronic version].