A new study reveals that the whooping cough spread is being caused mainly by children, leading experts to conclude that large immunization campaigns aimed at teenagers and adults may have minimal impact, Michigan University researchers wrote in the journal Science today. Many have believed that the pertussis (whooping cough) outbreak in California and some other US states is caused chiefly by adult transmission - a notion that might be completely misguided. Advising seniors to be given the Tdap booster vaccine (tetanus, diphtheria and pertussis), which a US advisory panel did recently, may be targeting the wrong people, say the authors.

The CDPH (California Department of Public Health) announced that on 9th November, the number of reported whooping cough cases in 2010 surpassed the previous record in 1950. There have been 6,631 confirmed cases so far this year, compared to 6,613 in 1950.

Pejman Rohani and team examined a Swedish case. Authorities there stopped a pertussis immunization campaign because of concerns about safety. Routine vaccinations were suspended for 17 years. However, the Swedish health ministry continued filing data on whooping cough incidences. This data was also available according to age.

The Swedish data was compared to a European study involving 7,000 individuals in eight countries in 2008.

With the help of special computer software, the researchers combined both sets of data to determine how whooping cough is spread according to age groups.

The investigators discovered that whooping cough rates only fell significantly when the routine vaccination of children was resumed. Pertussis incidence went down considerably in all age groups, except for teenagers.

Because of their behavioral characteristics, children physically interact mainly with other kids. Their chances of infecting each other are far greater than becoming infected from an adult, the authors explained.

If a large proportion of children are immunized, the protective effect for all children is huge. Infected adults play a very minor role in transmitting whooping cough to children, the researchers added.

The authors concluded: Ignoring age-structured contacts is likely to result in misinterpretation of epidemiological data and potentially costly policy missteps. Pertussis, or whooping cough is a highly contagious respiratory infection caused by Bordetella pertussis a bacterium. Infected individuals usually have a violent and uncontrollable cough. After bouts of coughing the patient may gasp for air, as they take in deep breaths the hallmark whooping sound is heard. Coughing fits can occur regularly for up to ten weeks or more, hence the disease's nickname, the the 100 day cough. Babies and very young children are particularly vulnerable to whooping cough complications, which for very young babies can be fatal.

Experts worldwide stress that the best way to protect yourself and society from pertussis is to take the vaccination.

Approximately 30 to 50 million people become infected globally each year, of which about 300,000 die, according to the CDC (Center for Disease Control and Prevention). Over half of all babies under the age of 1 year who become infected need to be admitted to hospital.

"Contact Network Structure Explains the Changing Epidemiology of Pertussis"
Pejman Rohani, Xue Zhong, Aaron A. King
Science 12 November 2010: Vol. 330. no. 6006, pp. 982 - 985 DOI: 10.1126/science.1194134