Update on California Outbreak of Pertussis, 2010
Abstract & Commentary
By Mary-Louise Scully, MD
Dr. Scully is Director, Travel and Tropical Medicine Center, Sansum Clinic, Santa Barbara, CA.
Dr. Scully reports no financial relationships relevant to this field of study.
Synopsis: As of early September 2010, California has reported a seven-fold increase in cases of pertussis compared to the previous time period in 2009 and the highest number of cases reported in 52 years. Eight deaths have occurred, with the majority in infants younger than 2 months of age. Recommendations for the use of tetanus-diphtheria-pertussis (Tdap) vaccine have been updated for California in the setting of this outbreak.
Source: Number of Pertussis Cases in California. Pertussis Summary Report (Sept. 7, 2010). California Department of Public Health (CDPH), Immunization Branch. http://www.cdph.ca.gov/HealthInfo/discond/Pages/Pertussis.aspx. Accessed September 11, 2010.
As of September 7, 2010, there have been 3,834 (confirmed, probable, and suspected) cases of pertussis reported in California. This represents a seven-fold increase over 2009, when only 530 cases were reported. Historically, the most recent peak in California pertussis activity was in 2005, with 3,182 cases reported. Prior to that it had been 52 years since the numbers had been in this range, with 3,837 cases reported in 1958.
Eight deaths have occurred, and seven of these were in infants younger than 2 months of age who had not received any doses of pertussis-containing vaccine. The other infant death occurred in a 28-week premature infant who had received one dose of DTaP (diphtheria, tetanus, and pertussis vaccine) at age 2 months, but who was only 11 days before the onset of clinical illness.
Of the cases with known hospitalization information, 59% of hospitalized cases were younger than 3 months of age, and 74% were infants less than 6 months of age. In terms of pertussis rates by race/ethnicity, the overall rates remain highest in whites (8.9/100,000), but age-specific rates show that the highest rates are in Hispanic infants younger than 6 months of age (222/100,000).
Fifty-five out of 61 counties (or local health jurisdictions) in California have reported at least one pertussis case, with a median case rate by county of 8.8 per 100,000 (range 0-121). San Luis Obispo and Marin counties have the highest rates so far, with 121 and 115 per 100,000, respectively.
Commentary
In light of this outbreak, the California Department of Public Health (CDPH), Immunization Branch, has issued updated 2010 Pertussis Vaccination Recommendations.1 The most notable changes are those regarding pregnant woman, children 7-9 years of age, adults older than 65, as well as elimination of any minimal interval between receipt of Td and Tdap.
Woman of childbearing age should be vaccinated with Tdap, preferably before pregnancy, and the Advisory Committee on Immunization Practices (ACIP) prefers vaccination in the immediate post-partum period. However, pregnancy is not a contraindication for vaccination, and the American Academy of Pediatrics (AAP) recommends that unimmunized pregnant adolescents be given the same consideration for Tdap as non-pregnant adolescents. The American College of Obstetrics and Gynecology (ACOG) and ACIP recommend that if Tdap is given during pregnancy, it be given during the second or third trimester to minimize the coincidental association of Tdap vaccination with adverse outcomes, which occur most often during the first trimester.
The CDPH recommends that all patients indicated for immunization against tetanus, diphtheria, or pertussis be immunized with DTaP if age 6 weeks to 6 years, i.e., providers can begin DTaP as early as 6 weeks and proceed with the DTaP schedule at 4-week intervals. For children ages 7-9 years, Tdap is now recommended. This use is beyond the licensed age group, but existing data suggest that the use of Tdap at these ages is safe.2,3 In Canada, for example, Tdap is licensed for ages 4 and older. In addition, Tdap (instead of Td or TT) should be used for wound management in any patient 7 years or older.
In addition to stressing the importance of immunizing all health care personnel with direct contact with infants and pregnant woman at birth hospitals, the CDPH is also targeting other close contacts of infants, especially parents, siblings, and caregivers of infants. Older adults, especially grandparents, are often an important part of an infant's early exposures. CDPH is now recommending Tdap administration to persons 65 years of age and older even though published data on the safety and efficacy in this age group are limited and this represents use beyond the licensed age group for Tdap. However, in the setting of the outbreak, it is felt that any additional protection of these older adults would protect vulnerable infants.
Ideally, vaccination with Tdap should occur two weeks before contact with an at-risk infant. Since pertussis immunity from immunization or even natural disease wanes over time, children who were vaccinated before kindergarten are often susceptible again by early adolescence. Therefore, middle-school children ages 10-13 who have not received a pertussis vaccination since age 4-6 years should receive Tdap. Providers are being encouraged to offer Tdap at pre-teen and adolescent visits.
One of the frequently asked questions during the initial California outbreak was regarding the minimum interval between prior receipt of Td and receiving another Tdap. When the risk of contracting pertussis is elevated, both ACIP and AAP recommendations permit any interval between doses of Td and Tdap. Concerns about an increased local reaction at the injection site after more recent prior doses of Td or DTaP exist, but this was not found to be the case in more recent studies and reports.2,4 Therefore, any recent prior Td or any undocumented history of prior Td or Tdap, should not be a valid reason to withhold Tdap.
Another facet of prevention to curb pertussis outbreaks is post-exposure chemoprophylaxis of close contacts of confirmed or probable cases, including household contacts and health care professionals. Azithromycin for 5 days should be prescribed (i.e., prophylaxis and treatment regimens are the same). All cases and contacts under treatment should self-isolate for 5 days and, in particular, no one should return to work or school until the 5-day course of azithromycin is complete in order to reduce transmission. More information on prescribing recommendations and useful information on the specific definition of pertussis "close contacts" can be found at http://www.cdph.ca.gov/HealthInfo/discond/Pages/Pertussis.aspx under CDPH Quicksheet: Pertussis.
Although these recommendations are specifically for California in the setting of this 2010 outbreak, they may be predictive of upcoming and expanded changes for the use of Tdap in children ages 7-9 and adults older than 65 when the ACIP revises its recommendations. In the meantime, the new CDPH recommendations are reassuring to health care providers and travel medicine physicians who were already using Tdap "off label" in many patients older than age 65, especially those older patients caring for, living with, or traveling with family and relatives with young infants and adolescents.
References
- California Department of Public health (CDPH), Immunization Branch. Pertussis Immunization Policy July 2010. http://www.cdph.ca.gov/HealthInfo/discond/Pages/Pertussis.aspx. Accessed September 11, 2010.
- Halperin SA, et al. How soon after a prior tetanus-diphtheria vaccination can one gisve adult formulation tetanus-diphtheria-acellular pertussis vaccine? Pediatr Infect Dis J 2006;25:195-200.
- Scheifele DW, et al. A modified vaccine reduces the rate of large injection site reaction to the preschool booster dose of diphtheria-tetanus-acellular pertussis vaccine. Pediatr Infect Dis J 2005:24(12):1059-1066.
- Iskander J. Immunization Safety Office Surveillance Updates, ACIP Meeting, February 2007.
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