Whoop, There It Is - Pertussis in the United States
Sarah Villarreal, Pharm.D., Besu Teshome, Pharm.D., and Jennifer K. Seltzer, Pharm. D.
September 10, 2012
Pertussis is a vaccine-preventable disease in the United States currently experiencing a substantial rise in incidence. From January 2012 to July 2012, 37 states have had an increase in the reported number of cases compared with the same time period in the previous year.1 Washington State cited an increase from 253 cases to 3,285 cases and Minnesota described an increase from 661 cases to 1,881 cases. Texas has identified 500 cases as of July 2012, which is twice as many as that reported in 2011 during the same time period.1-3 According to the Centers for Disease Control (CDC), more than 17,000 cases of pertussis have been reported nationwide through July 2012, including 9 deaths.1
Sydenham4 coined the term, pertussis, in 1679 from the Latin term meaning "intense cough." The highly contagious respiratory infection is also known as "whooping cough" due to the inspiratory "whoop" sound some patients make after coughing. This disease is caused by the gram-negative coccobacillus, Bordetella pertussis.4 Using only humans as its reservoir, this bacterial infection can quickly spread from person to person. Symptoms become evident after 7-10 days of exposure and usually last up to six weeks. Clinical manifestations are categorized in three phases: the catarrhal phase, the paroxysmal phase, and the convalescent phase. Initial symptoms in the catarrhal phase are synonymous with the common cold, allowing a pertussis infection to remain undiagnosed for 1-2 weeks, although the incubation period for the common cold is typically shorter (i.e., 1-3 days). The key distinction for pertussis infections is a severe cough, which marks the beginning of the paroxysmal phase and persists for several weeks to several months. 1,4-6 Other symptoms common in this phase include an inspiratory "whooping" sound following a coughing episode and post-tussive emesis. The convalescent phase is marked by reduced cough frequency and severity, which typically lasts for one to two weeks. Total duration of a pertussis infection is approximately three months. Although this infection can occur in people of all ages, infants experience the highest mortality risk and more than half of those infected will be hospitalized. Of those hospitalized, 67% will experience apneic episodes, 23% will develop pneumonia, and 1.6% will die from pertussis complications.1,5 In adolescents and adults, the overall symptoms can be less intense and the inspiratory "whoop" may not b e present. However, adolescents and adults may also experience complications including weight loss, loss of bladder control, fainting, and rib fractures due to coughing.1,6
The goal of treatment is to decrease symptom severity as well as decrease the spread of infection. Early treatment (within 2 weeks of symptom onset), which is key, may be based off clinical suspicion and later confirmed with cultures. Macrolide antibiotics are the gold standard for treatment but, unfortunately, the non-specific symptoms prevent patients from receiving antimicrobials in a timely fashion. However, antibiotics may still reduce disease spread.1, 5, 6
Due to the difficulty of effectively treating these patients, vaccinations provide the best means to prevent pertussis dissemination. Initial vaccinations were made using whole cell pertussis, but the adverse effects associated with this formulation (e.g., seizures and encephalopathy) led to the development of acellular pertussis vaccines. These acellular vaccines contain purified pertussis antigens, which are associated with less severe, less frequent adverse events.1, 5 In a letter to the editor, researchers in Australia postulate the pertussis resurgence is due to the exchange from the whole cell pertussis vaccination to the acellular pertussis vaccine.7 Researchers evaluated children (n = 40,694) receiving any pertussis vaccination between 1999 and 2011. Children receiving a three-dose diphtheria, tetanus, and acellular pertussis (DTaP) vaccine as a primary course were found to have higher pertussis rat es than those who received the whole cellular pertussis vaccine regimen. This study also evaluated those receiving a mixed course and showed the incidence rates to be higher in those receiving DTaP as the first dose.7
In the United States, DTaP is the recommended vaccination for infants and is administered utilizing a five-vaccination schedule followed by a one-time booster shot of Tdap (tetanus toxoid, reduced diphtheria toxoid, acellular pertussis), which has a reduced amount of diphtheria and pertussis, between ages 11 and 12. In adolescents and adults, prior illness or vaccination may attenuate symptoms but do not confer life-long immunity. The recommended immunization schedule for adults who have not received Tdap is a one-time booster shot of Tdap between 19-64 years of age and an additional Tdap dose for those older than 65 years if in contact with children < 12 months old. 1,5,6,8-10
The current pertussis vaccine schedule is summarized in Table 1. Additional information regarding pertussis and pertussis vaccinations can be obtained from the CDC website (www.cdc.gov).Table 1. 2012 Recommended Pertussis Immunization Schedule8,9
|Age||2 mo||4 mo||6 mo||15 mo||18 mo||4-6 yrs||11-12 yrs||19-64 yrs||>65 yrs|
Pertussis is a commonly occurring respiratory disease with increased incidences in the United States. While this illness afflicts the entire population, the most severe symptoms and life threatening complications are highest in those less than 1 year of age. Although this infection can be treatable if caught early, vaccinations remain the superior method of preventing the spread of this disease.