Division of Bacterial Diseases (DBD) News Bulletin

Exploring Meningococcal Outbreaks and Carriage with Whole Genome Sequencing

Photo: Marsenia Harrison, in DBD’s Pertussis and Diphtheria Laboratory, examines agar plates inoculated with oropharyngeal swabs for bacterial growth from the Rhode Island outbreak, February 2015.

Typically, there is less than a one in a million chance of getting serogroup B meningococcal disease. However, in February 2015, students at a small university in Rhode Island found their odds increasing to approximately one out of every 2,500 after just two students, with no known contact to each other, came down with the disease. Soon after, a separate outbreak of serogroup B meningococcal disease occurred at a large university in Oregon. Over the course of four months, these outbreaks sickened nine individuals and tragically resulted in one death.

Between October 2014 and January 2015, two serogroup B meningococcal (MenB) vaccines were licensed in the United States allowing universities to quickly respond to outbreaks by vaccinating their students. These vaccines help protect against one type of the germ that causes meningococcal disease, Neisseria meningitidis serogroup B.

An important benefit of some vaccines is their ability to also protect against the carriage of germs, which can lead to the establishment of herd immunity. Carriage is when people have N. meningitidis in the back of their nose and throat with no signs or symptoms of disease. It is believed that about one out of every 10 people carry N. meningitidis, but it is not known if the new MenB vaccines affect carriage. Vaccine campaigns at these universities in response to these two outbreaks offered a unique opportunity to observe the effects of MenB vaccination on carriage, identify the germs in circulation, and investigate general carriage rates of N. meningitidis among U.S. college students.

However, performing carriage studies in no easy task. In this case, it required analyzing thousands of samples collected from students. In the past, a lab technique known as pulse-field gel electrophoresis (PFGE) was used to compare the DNA of N. meningitidis strains to see if there were genetic links. This process is time-consuming, labor intensive, and limited in the results it can provide. DBD’s Bacterial Meningitis Laboratory, with aid from the Biotechnology Core Facility Branch and National Center for Immunization and Respiratory Diseases’ Bioinformatics Support Team, investigated the two outbreaks and subsequent carriage studies using whole genome sequencing (WGS) in order to better understand outbreak strains and carriage at these
universities. WGS allowed for more sophisticated, in-depth strain comparison between the germs found in carriers and those that caused the outbreak. WGS also allowed the lab to see if there is any connection to strains that have been seen on other college campuses in the past few years.

“Both on-site and in-house processing of the samples required dedication and long hours of work every day and night,” recalls DBD’s Bacterial Meningitis Laboratory Director Xin Wang. “The Bacterial Meningitis Laboratory team and participating members from the Microbial Pathogenesis and Immune Response and Pertussis and Diphtheria Laboratories rose to the challenge and completed the work quickly.”

A final round of each carriage study will be held in fall 2015, at which point, CDC will look to see if the new MenB vaccines have had an impact on the carriage of N. meningitidis.