Special Feature

Pertussis Prevention

By Stan Deresinski, MD, FACP, Clinical Professor of Medicine, Stanford, Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center. Dr. Deresinski does research for the National Institutes of Health, and is a consultant and an advisory board member for Merck. This article originally appeared in the November 2010 issue of Infectious Disease Alert. At that time it was reviewed by Timothy Jenkins, MD, Assistant Professor of Medicine, University of Colorado, Denver, Denver Health Medical Center. Dr. Jenkins reports no financial relationship to this field of study.

The introduction of acellular pertussis vaccines represented an important advance in public health, but developing a vaccine is not synonymous with protecting a population. The latter involves convincing health care providers (HCPs) and the targeted populations of its safety and efficacy and making the vaccine readily available. The uptake of the pertussis vaccine is somewhat complicated by the fact that it is only available in combination with diphtheria and tetanus toxoids — DTaP is licensed for infants and young children and Tdap (tetanus, diphtheria, acellular pertussis) for those 10-64 years of age. The Advisory Committee on Immunization Practices (ACIP) in 2005 recommended that Tdap replace the standard TD for the latter group.

The CDC has analyzed data from the National Health Interview Survey (NHIS), and found that the self-reported tetanus vaccination coverage was 60.4% in 1999 and 61.6% in 2008 among adults ages 18-64 years.1 Of those reporting vaccination during 2005-2008, 52% reported receiving Tdap, but total Tdap coverage in 2008 was only 5.9%. Even worse, only 15.9% of HCP and 5.0% of individuals with infant contact reported having received Tdap.

The effects of these low reported rates of uptake of Tdap are reflected in the current situation in California. As of August 24, a total of 3311 confirmed, probable, and suspected cases had been reported during 2010, corresponding to a rate of 8.5 cases/100,000 population.2 This was a seven-fold increase from the number of reported cases during the same time period in 2009, when just 454 cases were reported, and is the largest number of cases in California since 1958. Case rates were highest in infants < 6 months of age (158 cases/100,000), and in children aged 7-9 years (26 cases/100,000), and adolescents aged 10-18 years (20 cases/100,000). Twelve percent of cases have required hospitalization. Sixty percent of hospitalized patients were infants < 3 months of age, with three-fourths of these being < 6 months of age. Eight deaths have been reported, seven of which were in infants < 2 months of age at time of disease onset; none had received any doses of pertussis-containing vaccine. The eighth fatality was a 28-week preemie who was 2 months of age and had received the first dose of DTaP 11 days prior to disease onset.

Pertussis (whooping cough) is spread by inhalation of respiratory droplets or aerosols and is highly contagious — each patient is believed to infect, on average, more than a dozen individuals, and infants are highly vulnerable. Infants are protected from many infections during their first months of life as the result of the transfer of maternal antibodies during gestation. Unfortunately, unless recently immunized, most pregnant women have waning of immunity to pertussis and are unable to provide sufficient protective antibody to their fetus. As a consequence, the California Department of Public Health (CDPH) recommends that all women of childbearing years be vaccinated with Tdap vaccine. Pregnancy is not a contraindication to vaccination,3 although vaccination is commonly deferred until the 2nd or 3rd trimester, or immediately postpartum. In addition, all other close contacts of infants, including family members, caregivers, and HCPs, should also be vaccinated at least 2 weeks before contact. CDPH recommends that all health care personnel, particularly those who have direct contact with infants and pregnant women, be immunized with Tdap to protect their patients and themselves. This strategy provides a "cocoon" of safety for the infant.

The first dose of DTaP, the vaccine version for infants and young children, has been typically given at 2 months of age but may be given as early as 6 weeks to provide protection earlier in life. CDPH recommends that vaccination with Tdap include critical groups for whom Tdap is not licensed, including children 7-9 years of age and individuals ≥ 65 years of age. Children 7-9 years of age who had not received all of their routine childhood DTaP vaccine doses are recommended to receive Tdap. Vaccination of those ≥ 65 years of age is important because of the potential role of grandparents in transmission to infants. Pertussis in adults usually does not have the severe whooping cough characteristically seen in infants and young children and, as a consequence, frequently goes undiagnosed. Nasopharyngeal cultures are the gold standard for diagnosis, but are quite insensitive; the optimal single test is detection of Bordetella pertussis nucleic acid by PCR. Serological testing is generally not recommended.

Because of its lack of licensure in those > 65 years of age, questions have arisen regarding Medicare coverage. Tdap vaccine is covered by Medicare Part D, and may be obtained by Part D beneficiaries from a network pharmacy without out-of-pocket costs to the beneficiary. Tdap may also be provided in a network provider's office; however, this would require the beneficiary to pay for the vaccine costs up front and then be reimbursed by his or her Medicare Part D plan. It is recommended that beneficiaries contact their Medicare Part D plan in advance for detailed instructions on reimbursement for Tdap vaccination.

The resurgence of pertussis is a reminder that we have not conquered all childhood diseases in the United States. Reasons for the continuing and worsening pertussis problem include the lack of lasting immunity after vaccination (as well as after natural infection), the lack of passively transferred protective antibody in most infants, and the role of adults as reservoirs for transmission. As HCPs, we all have an obligation to actively promote pertussis vaccination, including for ourselves, to protect our patients and families.

References

1. Centers for Disease Control and Prevention. Tetanus and pertussis and vaccination coverage among adults aged ≥ 18 years — United States, 1999 and 2008. MMWR Morb Mortal Wkly Rep 2010;59:1302-1306.

2. California Department of Public Health. Pertussis Report 8/24/10. Available at: www.cdph.ca.gov/programs/immunize/Documents/Pertussis%20report%208-24-2010%20-%20For%20Release.pdf.

3. California Department of Public Health. Pertussis Vaccination Recommendations 2010. Available at: http://eziz.org/PDF/CDPH%20Pertussis%20Immunization%20Policy%20July%202010.pdf.