180

 

 

My weight has gone up and down most of my life. I was a chubby kid, a skinny teenager, and I put weight on and off throughout my adult life. About a year before Andrew was born, I stepped on a scale at a clinic where I was volunteering and was not able to get my weight. The scale would only weigh up to 300 pounds. My body mass index (BMI) was 39 kg/m². My waist size was more than 40 inches, which meant that I was at very high risk for cardiovascular disease and type II diabetes. In 2014, I had a physical exam before going to Sierra Leone. I weighed 284 lbs. I’d lost around 20 lbs. and felt pretty good about that. Nevertheless, my fasting blood glucose was still over 100 mg/dL, which meant I had prediabetes.

 

Although she's no longer "in the business," Holly, my wife, is a professional photographer and knows how to make people look good. I went to Africa twice in 2014 and was bothered when I saw photographs of myself taken by other people. I didn't realize how bad I looked. I was 52 years old and had a two-year-old son. I realized that, if I wanted to see Andrew reach adulthood, I needed to get my weight under control.

 

Haydom, Tanzania 2014

I had been riding a bicycle for many years. I was riding 100 miles per week when Holly and I lived in New Orleans, but New Orleans is flat. The biggest "hills" I had to climb were the levee and I-10 overpasses. When we moved back to the Pacific Northwest I had get used to not only hills, but cold, wet winter weather. That took a couple of years.

 

I started pushing myself; riding more miles, riding up hills that I had previously avoided, and riding in miserable weather. I also changed my diet, although not drastically. I cut down on carbohydrates and ate more salads. I bought a rowing machine so that I could keep up my workouts during the winter months when it was too cold or wet to ride. I started keeping track of my weight and used an app on my cell phone to track my rides.

 

I took some long rides in the summer. In July 2016, I took a couple of days to ride the Olympic Discovery Trail from Port Townsend to La Push, Washington. In June of this year I rode from Tacoma, through Seattle to the Snohomish County line, around Lake Sammamish, then through Renton, Black Diamond, Enumclaw, Buckley, Puyallup, and back to Tacoma. To celebrate my 55^th birthday, I rode from Tacoma to the coast and back.

 

June 2017

 

July 2017

 

In September 2015, my BMI dropped below 30 kg/m² - overweight, but no longer obese. A year later my BMI was less than 25: normal weight. This September the scale dipped below 180 lbs (BMI 23.1). My total cholesterol and triglycerides dropped, my high-density lipoprotein (HDL; "good" cholesterol) is up, and my fasting blood sugar is below 100 mg/dL.

 

 

 

I rode through last winter, but that put a lot of wear and tear on my bicycle. Now that I've achieved my weight loss goal, I've decided to start working on strength training this winter. I picked up a set of weights and read a book titled "Weight training for cyclists."

 

This hasn't been easy. It's been a huge commitment of time. So far this year I've spent 478 hours riding my bicycle, which doesn't include most of my rides to and from work. It's also been expensive. I bought a new bicycle last year and have had to replace a lot of parts and buy tools so that I can work on my bicycle instead of paying someone else to do it. I've also had to buy new clothes. The clothes I bought last year are too big for me now.

Replacing brake pads

 

I could not have done this without Holly's help. She has graciously allowed me to take the time I need to ride as much as I have. In return, she gets a healthier husband and Andrew gets a daddy who can keep up with him!

 

 

One final note: I've put my background in neuroscience nursing, public health, and bicycling to use as a member of the Cooper Jones bicyclist safety advisory council. One of our objectives is to encourage more people in Washington State to ride bicycles by making cycling safer. You can read more about it on the Washington Bikes website.

Andrew with his uncle Seth. I met Holly while I was taking care of Seth who had a traumatic brain injury in a motor vehicle accident.

 

 

 

 

 

 

 

Mumps

I’ve intended to write about mumps for nearly a year. Parenting and bicycle riding have taken my time and attention away from this blog. More about that later.

 

It was about this time last year that our mumps epidemic started. Over a four month period we had 59 confirmed and probable mumps cases. We investigated an additional 118 suspect cases and 52 people who did not meet one of those three classifications and were ruled out for mumps. That and a bad influenza season kept my colleagues and me busy! Other jurisdictions had far more cases than we did. King and Spokane counties in Washington State each had more than 300 confirmed and probable cases. Arkansas had nearly 3,000 cases.

 

Mumps is a viral disease characterized by swelling of the parotid salivary glands, which are on the side of the face in front of the ear. One or both parotid glands may be swollen and sometimes other salivary glands are swollen. The parotid gland may become so large that the swelling covers jawline extends to the neck.

 



CDC

 



CDC

The photographs above are from the Center for Disease Control and Prevention (CDC) Public Health Image Library. The first shows "characteristic swollen neck region." This is the photograph that is on the CDC's mumps webpage. The caption of the second photograph reads, "cervical [neck] swelling due to enlargement of the submaxillary salivary glands." What is not clear in either of these photographs is swelling of the salivary glands on the side of the face. The submaxillary glands are under the jaw and can be swollen with mumps, but it's rare that swelling of other salivary glands occurs without swelling of the parotid glands. Neck swelling can be caused by inflamed lymph nodes (lymphadenopathy), so not everything that looks like mumps is mumps.

 

Other symptoms of mumps include orchitis (painful swelling of the testicles), oophoritis (painful swelling of the ovaries), meningitis, and encephalitis. In fact, before the vaccine was developed, mumps virus was the most common cause of encephalitis in the United States. Permanent deafness in one ear is an uncommon complication of mumps. About one third of people infected with mumps virus have no symptoms but can still transmit it to others.

 

Parotitis can be caused by other things, including bacteria and other viruses. When mumps virus is not circulating in a community, sporadic cases of parotitis are likely to be caused by a virus other than mumps. There are also non-infectious causes of parotitis. Again, not everything that looks like mumps is mumps.

 

Mumps is the second M in MMR: measles, mumps, and rubella vaccine. Mumps outbreaks are uncommon in the U.S. because most states require children to have two doses of MMR by the time they start kindergarten. A few states require only measles vaccine or measles and rubella vaccine but, because MMR and MMRV (varicella: chickenpox) are the only measles-containing vaccines licensed in the U.S., most children in this country have received two doses of mumps vaccine by the time they start kindergarten.

 

So, why do we have mumps outbreaks in the U.S.? As I wrote before, no vaccine is 100% effective. A single dose of mumps vaccine is around 78% effective at preventing mumps. Two doses is about 88% effective. There is also evidence that immunity from mumps vaccine wanes over time. Outbreaks usually occur in places where people live in close contact with each other like military barracks or college dorms. Mumps is transmitted by respiratory droplets, contact with people infected with the virus, and contact with objects that are contaminated with the virus (fomites).

 

Respiratory droplets (CDC/ Brian Judd)

I can’t say how effective MMR was at preventing mumps in Pierce County. As I wrote in my post on attack ratios, I need the denominators: the number of vaccinated people exposed to the virus and the number of unvaccinated people exposed to the virus. I also don’t have the numerators. Immunization records are available for most children in Pierce County but frequently not available for adults. What I can say is that very few cases of mumps could be attributed to transmission in schools in Pierce County. Most of our cases were linked to another person with mumps living in the same house or transmission in a setting other than a school in Pierce County, e.g., workplaces or schools in the Auburn School District where there was a large outbreak.

 

“MMR is banned in Japan!”

 

Not exactly.

 

A different mumps virus was included in the Japanese MMR. The Urabe AM9 mumps vaccine was associated with higher incidence of viral meningitis. Although viral meningitis is usually self-limiting and does not result in longterm problems, Japan now uses a measles and rubella (MR) combination vaccine without a mumps component. No increased risk of viral meningitis has been found with the Jeryl Lynn strain, the virus used in the MMR and MMRV vaccines license in the U.S. Incidentally, both viruses are named after the children from whom the viruses were taken. Jeryl Lynn is the daughter of Dr. Maurice Hilleman, who developed over 40 vaccines, including mumps.

 

Andrew started kindergarten this year.

 

 

 

 

 

More information:

 

CDC: Mumps cases and outbreaks

 

References:

 

Barskey, A. E., Juieng, P., Whitaker, B. L., Erdman, D. D., Oberste, M. S., Chern, S. W. et al. (2013). Viruses detected among sporadic cases of parotitis, United States, 2009-2011. Journal of Infectious Diseases, 208(12), doi:10.1093/infdis/jit408.

 

Campbell, J. R. (2014) Parotitis. In J. D. Cherry, G. J. Harrison, & S. L. Kaplan (Eds.) Feigin and Cherry’s textbook of pediatric infectious diseases, 7^th Ed. [Electronic version]: Saunders.

 

Davidkin, I., Jokinen, S., Paananen, A., & Peltola, H. (2005). Etiology of mumps-like illnesses in children and adolescents vaccinated for measles, mumps, and rubella. Journal of Infectious Diseases, 191(5), doi:10.1086/427338.

 

Hatchette, T. F,. Mahony, J. B., Chong, S., & LeBlanc, J. J. (2009). Difficulty with mumps diagnosis: What is the contribution of mumps mimickers? Journal of Clinical Virology, 46(4), doi:10.1016/j.jcv.2009.09.024.

 

Litman, N. & Baum, S. G. (2015). Mumps virus. In J. E. Bennett, R. Dolin, & M. J. Blaser (Eds). Mandell, Douglas, and Bennett's principles and practice of infectious diseases, 8^th Ed. [Electronic version]. Saunders.

 

Parker Fiebelkorn, A., Barskey, A., Hickman, C,. & Bellini, W. (2012). Mumps. In S. W. Roush & L. M Baldy (Eds.) Manual for the surveillance of vaccine-preventable diseases, 5^th Ed. [Electronic version]. Center for Disease Control and Prevention.

 

Rubin, S. A. & Plotkin, S. A. (2018). Mumps vaccine. In S. A. Plotkin, W. A. Orenstein, P. A. Offit., & K. M. Edwards (Eds.). Vaccines, 7^th Ed. [Electronic version] Elsevier.

 

 

 

 

 

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:

 

Pertussis in Pierce County and Tdap During Pregnancy

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.

 

References:

 

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. http://pediatrics.aappublications.org/content/135/6/981.long.

 

American College of Nurse-Midwives. (2014). Position statement: immunization in pregnancy and p.ostpartum. http://midwife.org/ACNM/files/ACNMLibraryData/UPLOADFILENAME/000000000289/Immunization-in-Pregnancy-and-Postpartum-May-2014.pdf.

 

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. http://www.acog.org/Resources-And-Publications/Committee-Opinions/Committee-on-Obstetric-Practice/Update-on-Immunization-and-Pregnancy-Tetanus-Diphtheria-and-Pertussis-Vaccination.

 

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. http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(14)60686-3/fulltext.

 

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. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6207a4.htm.

 

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. http://cid.oxfordjournals.org/content/60/3/333.abstract.

 

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. http://cid.oxfordjournals.org/content/56/4/539.long.

 

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. http://pediatrics.aappublications.org/content/131/6/e1716.long.

 

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. http://www.jpeds.com/article/S0022-3476(12)00558-6/abstract.

 

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. http://cid.oxfordjournals.org/content/56/9/1248.long.

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, 7^th 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:

• Bicycle Helmets: What Every Parent Should Know
• Bicycle Safety: Myths and Facts
• Head Injuries and Bicycle Safety
• Bicycle Helmet Laws for Children
• Bicycle Helmets: American Academy of Pediatrics Policy Statement
• Bike Helmet Buying Guide

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.

References:

 

American Academy of Pediatrics. (2001). Bicycle helmets. Pediatrics, 108(4), 1030-1032. http://pediatrics.aappublications.org/content/108/4/1030.long

 

Attewell, R. G., Glase, K., & McFadden, M. (2001). Bicycle helmet efficacy: a meta-analysis. Accident Analysis and Prevention, 33(3), 345-352.

http://www.sciencedirect.com/science/article/pii/S0001457500000488

 

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. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6431a1.htm

 

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. http://online.liebertpub.com/doi/abs/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. http://pediatrics.aappublications.org/content/116/4/939

 

Markowitz, S. & Chatterji, P. (2015). Effects of bicycle helmet laws on children's injuries. Health Economics, 24(1), doi:10.1002/hec.2997. http://onlinelibrary.wiley.com/doi/10.1002/hec.2997/abstract

 

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. http://www.cmaj.ca/content/184/17/E921.long

 

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. http://onlinelibrary.wiley.com/wol1/doi/10.1002/14651858.CD001855/full

 

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. http://pediatrics.aappublications.org/content/122/3/605