Friday, June 10, 2016

Pertussis: waning immunity and Tdap during pregnancy

I've written several posts on pertussis (whooping cough) and pertussis vaccines over the last four years. I started my position in communicable disease epidemiology at the Tacoma-Pierce County Health Department at the beginning of the 2012 Washington State pertussis epidemic. Pertussis is a issue that has demanded a lot of our time and attention ever since.
This is an article that I wrote for our Communicable Disease and Immunization Update newsletter:
Historically, pertussis was thought of as a childhood disease. We now recognize that immunity to pertussis, through immunization or natural infection, wanes over time, and that the effectiveness of acellular pertussis vaccines wanes much more quickly than immunity from whole-cell pertussis vaccines. A case-control study reviewing data from the 2012 pertussis epidemic in Washington State demonstrated that, for children who had received all acellular pertussis vaccines, vaccine effectiveness was 73.1% within one year, 54.9% between one and two years, and 24.2% between two and three years (Acosta et al., 2015). Two studies of data from the 2010 pertussis epidemic in California demonstrated that children who received one or more doses of whole-cell pertussis vaccine were less likely to have polymerase chain reaction (PCR)-confirmed pertussis than children who had received all acellular pertussis vaccines (Klein et al., 2013; Witt et al., 2013).
The age distribution of pertussis cases in Pierce County in 2012 was similar to that in California in 2014 (Winter et al., 2014), with fewer cases at the ages at which pertussis vaccine booster doses are scheduled and fewer cases and lower incidence of pertussis in people born before 1997 who would have received at least one dose of whole-cell pertussis vaccine as part of their primary series.
Infants too young to receive pertussis-containing vaccine are at highest risk for complications and death from pertussis. During the 2012 epidemic, the incidence of pertussis in Pierce County and Washington State was highest in children under one year of age. Of the 15 Pierce County residents hospitalized for pertussis in 2012, 12 (80%) were under one year of age and 11 of those were under 6 months of age, too young to have received 3 doses of DTaP.
In 2015, 5 Pierce County residents were hospitalized for pertussis, three of whom were infants less than 2 months of age. Two of the mothers of those babies did not receive the recommended dose of tetanus, diphtheria, and acellular pertussis vaccine (Tdap) during pregnancy.
Case Series:
Case 1: Two-month-old girl with worsening cough admitted for observation with PCR-confirmed pertussis. Her mother received Tdap during pregnancy. While hospitalized, the infant had mild desaturations during coughing fits which quickly resolved without intervention. The baby was observed on the pediatric unit, not intensive care unit (ICU), and was discharged home on day three.
Case 2: One-month-old girl admitted with repeated episodes of desaturation and bradycardia. On the second day after admission, the baby was intubated and mechanically ventilated with sedation and chemical paralysis. She spent 8 days intubated, 11 days in the pediatric intensive care unit (PICU), and was discharged to home on day 15. Her mother did not receive Tdap during pregnancy.
Case 3: Three-week-old girl admitted after an episode of choking cough, apnea and cyanosis. Although the obstetric care provider recommended that her mother get a Tdap at the pharmacy, she did not receive one. The baby spent 3 weeks in PICU and was discharged four weeks after admission.
Although this sample is not representative, it is notable that the child whose mother received Tdap during pregnancy was not admitted to the PICU and had the shortest length of stay.
Antibody titers in adults who receive Tdap also wane. Healy et al. (2013) found that titers of pertussis-specific antibodies in cord blood from mothers who had received Tdap before or early in pregnancy were unlikely to provide adequate protection against infection for their newborn infants. In October 2012, the CDC's Advisory Committee on Immunization Practices (ACIP) recommended Tdap at 27 to 36 weeks of gestation with every pregnancy based on studies of paired maternal and cord blood from women who received Tdap during pregnancy. The American College of Obstetricians and Gynecologists (ACOG) and the American College of Nurse-Midwives support the ACIP recommendation.
Two studies conducted in the U.K. evaluated the effectiveness of maternal Tdap at preventing pertussis in infants too young to receive DTaP. Vaccine effectiveness was 93% for infants born to women who received Tdap in the third trimester (Dabrera et al., 2015) and 90% for infants younger than 2 months whose mothers received Tdap at least 1 week before birth (Amirthalingam et al., 2014).
Although estimates since the 2012 recommendation have not yet been published, uptake of Tdap during pregnancy has been lower than optimal. As part of a pilot project, the Washington State Department of Health is currently collecting data on Tdap during pregnancy from hospitals in selected counties, including Pierce. Data are preliminary, but, in 2014, less than 50% of women who delivered at Pierce County hospitals had a dose of Tdap during the pregnancy that was recorded in the hospitals' electronic medical record. Administering Tdap during a prenatal visit is the most effective way to ensure that a pregnant woman receives the dose. CDC recommends that providers who do not stock vaccines in their offices make a "strong referral" for vaccination. Resources supporting immunizing pregnant women are found on the ACOG, CDC, and Tacoma-Pierce County Health Department websites.

Acosta, A. M., DeBolt, C., Tasslimi, A., Lewis, M., Stewart, L. K., Misgades, L. K., et al. (2015). Tdap vaccine effective in adolescents during the 2012 Washington State pertussis epidemic. Pediatrics, 135(6). doi:10.1542/peds.2014-3358.
American College of Nurse-Midwives. (2014). Position statement: immunization in pregnancy and p.ostpartum.
American College of Obstetrics and Gynecologists. (2013). ACOG Committee Opinion No. 566: Update of immunization and pregnancy: tetanus, diphtheria, and pertussis vaccination. Obstetrics and Gynecology, 121(6). doi:10.1097/01.AOG.0000431054.33593.e3.
Amirthalingam, G., Andrews, N., Campbell, H., Ribeiro, S., Kara, E., Donegan, K., et al. (2014). Effectiveness of maternal pertussis vaccination in England: an observational study. Lancet, 384(9953). doi:10.1016/S0140-6736(14)60686-3.
Centers for Disease Control and Prevention. (2013). Updated recommendations for use of tetanus toxoid, reduced diphtheria, and acellular pertussis vaccine (Tdap) in pregnant women – Advisory Committee on Immunization Practices (ACIP), 2012. Morbidity and Mortality Weekly Report, 62(7), 131-135.
Dabrera, G., Amirthalingam, G., Andrews, N., Campbell, H., Ribeiro, S., Kara, E., et al. (2015). A case-control study to estimate the effectiveness of maternal pertussis vaccination in protecting newborn infants in England and Wales, 2012-2013. Clinical Infectious Diseases, 60(3). doi:10.1093/cid/ciu821.
Edwards, K. M. & Decker, M. D. (2013). Pertussis vaccines. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (6th Ed.). [Electronic version]. Elsevier.
Healy, C. M., Rench, M. A., & Baker, C. J. (2013). Importance of timing of maternal combines tetanus, diphtheria, and acellular pertussis (Tdap) immunization and protection of young infants. Clinical Infectious Diseases, 56(4). doi:10.1093/cid/cis923.
Klein, N. P., Bartlett, J., Fireman, B., Rowhani-Rahbar, A. & Baxter, R. (2013). Comparative effectiveness of acellular versus whole-cell pertussis vaccines in teenagers. Pediatrics, 131(6). doi:10.1542/peds.2012-3836.
Winter, K., Harriman, K., Zipprich, J., Schechter, R., Talarico, J., Watt, J., et al. (2012). California pertussis epidemic, 2010. Journal of Pediatrics, 161(6). doi:10.1016/j.jpeds.2012.05.041.
Witt, M. A., Arias, L., Katz, P. H., Truong, E. T., & Witt, D. J. (2013). Reduced risk of pertussis among persons ever vaccinated with whole cell pertussis vaccine compared to recipients of acellular pertussis vaccines in a large US cohort. Clinical Infectious Diseases, 56(9). doi:10.1093/cid/cit046.

Tuesday, June 7, 2016

Bicycle helmets

We've had great weather here in the Pacific Northwest. I usually don't start riding my bicycle to work until late April or May, but this year I started riding in February. I few weeks ago I rode the first segment of the Olympic Discovery Trail and plan to ride the entire 130 miles from Port Townsend to La Push later this summer (Yes Twilight fans, that's vampire and werewolf country).

In April I took a longer route home from work through an area of the city where I had not ridden before. My front wheel got stuck in a railroad track and I had a hard fall. I picked myself up, got back on my bike, and rode home. It wasn't until I got home and took my helmet off that I realized that I must have hit my head during the fall because my helmet was cracked from one side to the other.

I didn't remember hitting my head and didn't think much of it at the time. I had a huge bruise on my left hip, an abrasion on my left arm, and the impact to my helmet was on the left side; all consistent with falling on my left side. What wasn't consistent was the abrasion on my right knee and that the most significant damage to my bike was to the rear derailleur, which is on the right side of my bike.

I went to work the next day, which was probably a mistake. It wasn't until I was recounting the accident to my coworkers that I realized that I didn't remember the accident. I remembered getting my front wheel stuck in the railroad track, and I remembered getting on my bike and riding away. I remembered being a little dazed at the time, but I knew where I was, how I got there, and how to get home. I don't know if I lost consciousness, but there was a man in a pickup who kept asking if I wanted him to call 9-1-1. At the time, I was unaware of how serious my accident had been. I left work early and went to an urgent care to get myself checked out.
A concussion is defined as injury to the brain caused by a hard blow or violent shaking, producing a sudden and temporary impairment of brain function, such as a brief loss of consciousness or disturbance of vision and equilibrium.

The characteristic loss of consciousness is believed to result from rotational forces exerted on the upper midbrain and thalamus, impairing the function of the reticular neurons. Headache, nausea, dizziness, irritability, and impaired ability to concentrate can persist for days after the event. Persistence of these symptoms for weeks is called postconcussion syndrome and can last from 1 month to a year.

Stippler, M. (2016). Craniocerebral trauma. In R. B. Daroff, J. Jankovic, J. C. Mazziotta, & S. L. Pomeroy (Eds.) Bradley's neurology in clinical practice, 7th Ed. [Electronic version]. Elsevier.

As a neuro nurse, I know that even a minor brain injury can cause profound disabilities. The realization that I had a concussion frightened me. I kept wondering if my difficulty concentrating and irritability were postconcussion syndrome or because I had difficulty sleeping. I kept wondering if I had difficulty sleeping because of postconcussion syndrome or because I had a huge, painful bruise on my hip. What's most frightening is thinking what might have happened if I had not been wearing a helmet.

Like a lot of you, I grew up riding a bike without wearing a helmet. We all turned out okay, didn't we? Not all of us. A lot more children died in bicycle accidents in the past than now.

CDC, 2015
There are several reasons fewer children die in bicycle accidents now. One possibility is that children ride bicycles less frequently than in the past. Bicycle helmets reduce the risks injuries and death from bicycle accidents (Attewell et al., 2001; Hooten & Murad, 2014; Persaud et al., 2014; Thompson et al., 1999) and helmet laws are also associated with decreases in deaths from bicycle accidents (Markowitz & Chatterji, 2015; Wesson et al., 2008).

Like any preventive measure, bicycle helmets do not completely eliminate the risk of injury and death. The fact that I can't remember my accident is evidence of that, but I doubt that I would have been able to return to work as soon as I did, if at all, had I not been wearing a helmet.

This is the first time I've been in a serious bicycle accident since I was a teenager. It's also the first time I've had a concussion. It has been a frightening experience. As parents, we want to protect our children from serious injuries. Brain injuries can cause lifelong neurological deficits. Getting Andrew to wear a helmet during our rides together was challenging at first, but I love him too much to let him ride without one. Now it's just part of the routine.

Children are more likely to wear a bicycle helmet if they ride with an adult who does and less likely to wear a helmet if they ride with other children who do not (Khambalia et al., 2005), so set a good example for them.


Please see these references for more information about bicycle safety and helmets:

I'd like to thank the staff at Tacoma Performance Bicycle for getting me back on the road so quickly after I damaged my bike. They repaired my bike and had me out of the store in less than 30 minutes. Of course, I bought a new helmet while I was in there.

American Academy of Pediatrics. (2001). Bicycle helmets. Pediatrics, 108(4), 1030-1032.
Attewell, R. G., Glase, K., & McFadden, M. (2001). Bicycle helmet efficacy: a meta-analysis. Accident Analysis and Prevention, 33(3), 345-352.
Centers for Disease Control and Prevention. (2015). Bicycle deaths associated with motor vehicle traffic – United States, 1975-2012. Morbidity and Mortality Weekly Report, 64(31), 837-841.
Hooten, K. G. & Murad, G. J. A. (2014). Helmet use and cervical spine injury: a review of motorcycle, moped, and bicycle accidents at a level 1 trauma center. Journal of Neurotrauma, 31(15), doi:10.1089/neu.2013.3253.
Khambalia, A., MacArthur, C., & Parkin, P. C. (2005). Peer and adult companion helmet use is associated with bicycle use by children. Pediatrics, 116(4), 939-942.
Markowitz, S. & Chatterji, P. (2015). Effects of bicycle helmet laws on children's injuries. Health Economics, 24(1), doi:10.1002/hec.2997.
Persaud, N., Coleman, E., Zwolakowski, D., Lauwers, B., & Cass, D. (2012). Nonuse of bicycle helmets and risk of fatal head injury: a proportional mortality, case-control study. CMAJ, 184(17), doi:10.1503/cmaj.120988.
Thompson, D. C., Rivara, F., & Thompson, R. (1999). Helmets for preventing head and facial injuries in bicyclists. Cochrane Database of Systematic Reviews, 4, CD001855. doi:10.1002/14651858.CD001855.
Wesson, D. E., Stephens, D., Lam, K., Parsons, D., Spence, L., & Parkin, P. C. (2008). Trends in pediatric and adult bicycling deaths before and after passage of a bicycle helmet law. Pediatrics, 122(3), doi:10.1542/peds.2007-1776.