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What IS up with
whooping cough these days?

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ISHLT ID Council Communications Liaison
Professor of Pediatrics
St Louis Children's Hospital
St Louis, Missouri, USA

Community acquired respiratory infections are troublesome for solid organ transplant recipients, so why do we now have to worry about whooping cough? Wasn't that a disease of childhood that was eliminated with a vaccine? It nearly was by the 1980s but is making an impressive come back. What, when, where, and for heaven's sake why? And what should we do about it?

Whooping cough is caused by Bordetella pertussis, so named in 1679 because in Latin it means "intense cough" also known as "the hundred day cough" in Chinese. We humans are the only reservoir and can quite effectively spread the bacteria by aerosolized droplets. The incubation is usually 7-10 days. The major problem is that neither infection nor immunization produces lifelong immunity. Clinical disease begins with a mild URI, the catarrhal phase, and progresses to paroxysms of cough with the tell tale inspiratory whoop and emesis, the paroxysmal stage. Fever is absent or minimal. Immunized children and adults can have a mild, atypical cough that lasts for 6-10 weeks and unknowingly spreads the infection. The most severe disease occurs in infants < 6 months of age. Babies often present without the whoop but have apnea, bradycardia or gagging. Most of these infants are hospitalized, 22% develop pneumonia and 2% develop seizures. One percent of infants < 2 months of age will die.

Early in the 20th century, hundreds of thousands of cases of pertussis occurred in the US but the incidence declined dramatically with the licensure of DTP in 1949. As infants and children were widely immunized the disease became uncommon but since 1980 has been steadily increasing. By Oct 12, 2012 the CDC reported 32,600 cases and the yearly total is predicted to be the highest number since 1959. Since most cases are not reported, the actual number in the US is estimated to be over a million. The vast majority of states reported a 2 fold or higher increase in cases in 2012 compared to 2011. The rise has been most striking in the pediatric age group up through adolescence while the over 20 year olds (even those over 60) have not seen much increase.

Why? The CDC's investigation of a pertussis epidemic in Washington state earlier this year is quite revealing. Over 2,500 cases were identified and a valid vaccination history was available for 91% of patients aged 3 mo - 19 yrs. They found that the vast majority of cases were fully immunized against pertussis so this was not a failure of families to vaccinate their children. When they looked at the cases broken down by age, they concluded as have others, that the problem is actually waning immunity from the vaccine. The very successful DTP vaccine containing whole cell B. pertussis was replaced in the 1990s by vaccines containing acellular pertussis (DTaP or Tdap) to decrease the fever and irritability often seen with the whole cell preparation. It appears that the efficacy might wane after as little as 2-3 years. However, unvaccinated children have an 8 fold increased risk for pertussis than those fully immunized with DTaP. Vaccinated children are also less infectious, have milder and shorter illness, fewer complications, and fewer hospitalizations. So, while new vaccines are being investigated and booster doses discussed, timely and complete immunization is critical.

What can be done? Diagnosis of pertussis is by PCR and treatment is 5 days of azithromycin or clarithromycin. Once the paroxysmal stage begins, treatment does not influence duration or severity but does reduce transmission. Post-exposure management of household and other close contacts including child care is very important. Un or under immunized contacts should receive the age appropriate vaccine. Chemoprophylaxis with a macrolide is the same as treatment and works best if begun within 21 days of exposure. Of note, a contact should receive prophylaxis even if fully immunized if he is high risk for severe pertussis or lives in a household with people at high risk.

Finally, while it's important to make sure our transplant patients are fully immunized, everyone with close contact should be up to date as well. It is recommended that every adult receive a dose of Tdap. This includes parents, grandparents, care givers, and health care providers. Pertussis is likely to be an increasing threat to transplant recipients, so recognition and vigilance will be vital.

Disclosure Statement: The author has no conflicts of interest to disclose.