The Resurgence of Pertussis: Is Lack of Adult Vaccination to Blame?

February 23, 2011

By Ijeoma Ejigiri, Class of 2011

Faculty Peer Reviewed

Whooping cough. 100 day cough.  Pertussis.  These are the various names for the disease caused by the bacterium Bordetella pertussis.  This small gram-negative coccobacillus, transmitted via respiratory droplets, is responsible for causing coughing paroxysms followed by a long inspiratory gasp, during which the characteristic high-pitched “whoop” occurs.[1]  These coughing paroxysms can last for ten weeks or longer, hence the moniker “100 day cough.”   The paroxysmal phase is usually preceded by a prodromal illness that is typically indistinguishable from a viral upper respiratory infection.  While pertussis typically affects infants, adolescents and adults are susceptible as well.  Adults may not exhibit some of the typical manifestations of the disease, presumably due to partial immunity from previous infection or immunization.   In fact, the disease is often misdiagnosed as acute bronchitis or remains undiagnosed.[2]

During the 20th century pertussis was a major cause of morbidity and mortality among infants and children.  From 1922 to 1948, pertussis was the leading cause of death due to an infectious disease among American children younger than 14.[3]  With the advent of the whole-cell pertussis vaccine, the rates of pertussis infection dropped to an all-time low in 1976, with only 1010 reported cases.[4]  Currently, children in the United States are vaccinated with a combination vaccine, diphtheria-tetanus-acellular pertussis (DTaP).  Whole cell pertussis vaccines are not currently used in the United States, but are still used in other countries.  Adolescents and adults should receive a booster vaccine with the combination of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap).[5]

The incidence of pertussis changes in a cyclical fashion, with spikes occurring approximately every 5 years.[4]  Recently there has been a dramatic resurgence of pertussis in the United States.  Pertussis infection rates have been steadily rising since the 1980s.  In California during 2010 there were a total of 8383 reported cases of pertussis, the most since 1947.[6]  Outbreaks were also reported in Pennsylvania, New York, South Carolina, and Michigan.[7]

The cause of the resurgence of pertussis is thought to be multifactorial.  One hypothesis is that decreased rates of childhood vaccination are playing a role in this epidemic. There has been a growing anti-vaccine movement due to the concern of autism and other diseases associated with vaccine administration.  A study performed by the National Committee on Quality Assurance reported that DTaP vaccination rates dropped from 87.2% in 2008 to 85.4% in 2009.[8].  The San Francisco school systems are reporting remarkably low immunization rates due to parent concerns about vaccination.[7]

Adolescents and adults are important reservoirs of the bacteria.  Some have suggested that the majority of pertussis cases are occurring in adolescents and adults.   The Centers for Disease Control and Prevention (CDC) reported that pertussis infection rates in adolescents and adults rose from 19.8% in 1989 to 28% in 1994.[9]  These infection rates are likely underestimates, given that pertussis is often misdiagnosed in adolescents and adults, who often present atypically.[4]  Treatment is often delayed or inappropriate treatment is initiated. Adolescents and adults serve as a source of infection of pertussis for other household contacts, including small children.  In a recent study conducted in Sydney, Australia, during a pertussis outbreak in 2009, household contacts such as parents and siblings were identified as sources of infection for 60% of infants.[10]  Several other studies have identified parents, grandparents, adolescents, and even healthcare workers as significant sources of transmission to infants.[11]

This begs the question of why pertussis cases are rising among adult populations.  As mentioned above, the Tdap booster vaccine is recommended for adolescents and adults, and the immunity provided by this booster lasts approximately 10 to 12 years.  However, if adults do not obtain their booster vaccination as scheduled, waning immunity puts them at increased risk for pertussis infection. Cost and lack of access to healthcare are two reasons why adults are not receiving their vaccinations as scheduled. The elderly population is particularly susceptible to pertussis infection due to waning immunity; however, Medicare often does not reimburse for vaccination of adults against whooping cough, leaving this particularly vulnerable population to pay for the cost of vaccination out of pocket.[7]  Lack of awareness of the need of vaccinations among adults is also an issue. There is a perception that vaccinations are reserved for children.  In a recent survey of 1000 adults conducted by the National Foundation for Infectious Diseases, 40% of respondents said “they had vaccines as a child so they do not need them again” and 18% of respondents said “vaccines are not necessary for adults.”[12]

Clearly there is a need for better education about the importance of vaccination for adults, both for whooping cough and the other vaccine-preventable diseases.  According to the Department of Health and Human Services, 95% of the 50 000 Americans who die each year from vaccine-preventable diseases are adults.[13]  There are several efforts in place to help raise awareness of pertussis and encourage adult vaccination.  The vaccine maker, Sanofi-Aventis, is sponsoring public-service announcements on pertussis.  Also, the CDC has issued alerts on pertussis and provides many resources for health care professionals, parents, and patients desiring more information.[14]  Health care professionals at all levels should make concerted efforts to increase adult awareness of the need for vaccinations.

Dr. Ejigiri is a 4th year medical student at NYU School of Medicine

Peer reviewed by Vinh Pham, MD,  Assistant Professor of Medicine (Infectious Disease and Immunology), NYU Langone Medical Center

Image courtesy of Wikimedia Commons

References:

1. Hewlett E. Bordetella species. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases, 5th ed.  Philadelphia, PA: Churchill Livingstone;  2000:2701.

2. Hewlett EL, Edwards KM. Clinical practice. Pertussis–not just for kids. N Engl J Med. 2005;352(12):1215-1222.

3. Long SS. Pertussis. In: Nelson WE, ed. Textbook of Pediatrics. Philadelphia, PA: Saunders; 1996:779-784.

4. Black S. Epidemiology of pertussis. Pediatr Infect Dis J. 1997;16(4 Suppl):S85-89.

5. American Academy of Pediatrics. Pertussis. In: Pickering LK, Baker CJ, Kimberlin DW, Long SS, eds.  Red Book: 2009 Report of the Committee on Infectious Diseases, 28th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2009:504.

6. Centers for Disease Control and Prevention (CDC).  Pertussis outbreaks. http://www.cdc.gov/pertussis/outbreaks.html.  Accessed February 14, 2011.

7. Roehr B. Whooping cough outbreak hits several US states. BMJ. 2010;341:c4627.

8. National Committee for Quality Assurance.  The State of Health Care Quality. Reform, The Quality Agenda and Resource Use. 2010.  http://www.ncqa.org/Portals/0/State%20of%20Health%20Care/2010/SOHC%202010%20-%20Full.pdf. Accessed October 21, 2010.

9. Centers for Disease Control. Reported vaccine-preventable diseases: United States, 1993, and the Childhood Immunization Initiative. MMWR. 1994;43(04):57-60.

10. Jardine A, Conaty SJ, Lowbridge C, Staff M, Vally H. Who gives pertussis to infants? Source of infection for laboratory confirmed cases less than 12 months of age during an epidemic, Sydney, 2009. Commun Dis Intell. 2010;34(2):116-121.

11. Schellekens J, von König CH, Gardner P. Pertussis sources of infection and routes of transmission in the vaccination era. Pediatr Infect Dis J.  2005;24(5 Suppl):S19-24.

12. National Foundation for Infectious Diseases. American adults’ awareness about immunization. CARAVAN® omnibus surveys, conducted October 25–28, 2007, by Opinion Research Corporation. http://www.nfid.org/pdf/publications/adultimmcta.pdf. Accessed October 21, 2010.

13. Department of Health and Human Services. Centers for Medicare & Medicaid Services. Adult immunization overview. http://www.cms.hhs.gov/AdultImmunizations. Accessed June 24, 2008.

14. Centers for Disease Control. Pertussis (whooping cough) vaccination. http://www.cdc.gov/vaccines/vpd-vac/pertussis/default.htm.

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