Michigan Varicella Outbreak Associated with Riding a School Bus

A varicella outbreak that had occurred last year in Michigan is thought to be associated with riding on a school bus, which makes small, enclosed spaces, such as a school bus, a risk factor for both transmitting and acquiring airborne diseases, according to a recent press release by the Centers for Disease Control and Prevention (CDC).

A local kindergarten-grade 2 school located in Michigan notified Public Health-Muskegon County (PHMC) on the 3^rd of December last year to report that an 8-year-old student (referred to as the index patient) exhibited a rash that appeared to be varicella, otherwise known as chickenpox, and had been sent home.

Upon further investigation, PHMC found that the aforementioned student had four other siblings living in the household and not one of them had received their immunizations. Further investigation found that the student’s two older siblings and two younger siblings (ages 12, 25, 4, and 4 respectively) also exhibited rashes thought to be varicella on November 3, November 18 (2 siblings), and November 22 respectively. Furthermore, 7 weeks earlier, one of the parents of the household had received a diagnoses of herpes zoster, commonly known as shingles, on October 20, 2015. According to the press release, three days earlier, the parent sought treatment for “a painful, unilateral trunk rash” to which an antiviral drug called acyclovir had been prescribed. The CDC makes note that the index patient “was the first student on and the last off [the school bus] each day.” Three more students that rode the school bus with the index patient came to exhibit rashes associated with varicella and were diagnosed.

On December 15, the first student, 7 years of age, had exhibited the rash and after the use of “cutaneous lesion swab by polymerase chain reaction (PCR),” the student was diagnosed with varicella. Interestingly enough, the student had been fully immunized, but was reported to have ridden the same school bus as the index patient to and from school. On December 17^th and 23^rd, 2 students, also siblings, 7 and 5 years of age respectively, exhibited similar rashes to those aforementioned. Furthermore, their younger sibling, only 17 months old, started to exhibit the same rash later in the month, on December 28^th. The CDC found that out of the three cases, none of the students had received a varicella vaccination. Aside from these reported cases, there were no other varicella cases noted during that school year.

The CDC surmises that this may be due to the high vaccination rate experienced by the school. According to the press release, “The reported coverage with at least 1 dose of varicella vaccine in the school was 96% and for coverage with 2 doses was 95%. The overall coverage rate with all required immunizations for the school was 95%; 2% of children had waivers, and immunizations for 3% of children were incomplete.”

The CDC feels that overall, the nine varicella cases had begun with the adult case of herpes foster in the index patient’s household due to the fact that the all of the rashes occurred during the 10 to 21-day time frame that is typical of varicella.

Previous to this, an outbreak of varicella that had occurred in China, showed that transmission of varicella was not only plausible, but probable in small, enclosed spaces such as a school bus. The CDC feels that this case evidences the importance of varicella vaccinations, specifically 2-dose varicella vaccination, in order to reduce the odds of transmitting the disease to others and prevent further outbreaks. In addition, the CDC recommends that children between the ages of 12 and 15 months as well as between 4 to 6 years of age should receive these 2-dose varicella vaccinations. Anyone who suspects that they might be infected with varicella or herpes zoster should go to the doctor for immediate evalutation.