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What is Infectiousness? Infectiousness of a disease refers to the possibility of people exposed to the disease to later develop that disease.  Dangerous diseases like hepatitis B and AIDS are poorly infectious, because they are only transmitted by blood contact, or by sexual activity.   On the other hand, viral colds and chicken pox are very infectious, because the person with the disease is releasing large number of viruses into the air around him by coughing and sneezing.  Other children can get the disease by simply being in the same classroom as him for a school day.   Secondary attack rate is the proportion of susceptible persons exposed to a particular disease who will get the disease.  For example, if there are a hundred children in a class, and forty have been vaccinated against pertussis, then the number of susceptibles if sixty. Though pertussis is highly infectious, the champion is probably measles, with a secondary attack rate approaching 100%.  Chicken pox in the home setting is almost as bad, but this falls to 60-70% in the school setting.

Whooping Cough
(Pertussis)

The scientific name is pertussis (intense cough), but it is also known as the hundred days' cough. A cough doesn't sound very dangerous, but whooping cough is an awful disease.  A child unfortunate enough to get it suffers terribly for several weeks.

Whooping cough is caused by a bacterium, Bordetella pertussis.  The disease starts as a throat infection, with cold, cough, red eyes, and fever.  The cough gets worse and worse, and the diagnosis is usually made after a few days.

The cough occurs in prolonged bouts, during which the child is unable to breathe, and gets more and more anxious.  At the end of the bout, the struggling child draws in a deep breath with a loud whoop.  Not all children with pertussis have the characteristic whoop.  These bouts of cough are often followed by vomiting.  The cough is provoked by laughing, crying, and eating, making the child scared to do any of these.

The illness goes on for weeks, and most children lose weight, becoming malnourished.  The illness is associated with complications affecting several body organs, chiefly the brain and lungs.  Pneumonia, seizures, encephalopathy, bleeding into the brain, and bleeding in the eye are some of the complications.  It also allows old, quiescent tuberculosis to flare up.

Treatment

Though it is a bacterial disease, antibiotics are of small value in its treatment.  Once the disease has taken hold, antibiotics serve only to eradicate the infection and prevent spread.  The bouts of cough are not stopped by killing the bacteria.

Various cough syrups are tried in this disease, but give only partial relief.

This disease is highly infectious, with a secondary attack rate of 97%.  A vaccine is available for this disease, and is a part of the DTP vaccine.  This is one of the few diseases where antibodies from the mother do not cross the placenta.  Babies are thus unprotected against pertussis at birth, and can get it at very young ages.

There is much controversy about the side effects of the pertussis vaccine.  Though it has been proved that it does not cause brain damage, the fear persists.  A new type of whooping cough vaccine, called the acellular pertussis vaccine, has been available for some years now.  It has lesser side effects than the whole cell killed vaccine that we have been using.

Last revision: July 15, 2007

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