MS Clusters and Case Numbers A cluster of multiple sclerosis is the perception of very high number of cases of MS in a particular time and place. MS clusters may signal possible environmental or genetic risk factors that cause or trigger the disease. But so far, cluster studies have not produced clear evidence of any such factors. Investigating Clusters The process of investigating clusters of any disease, especially MS, is complicated. It is difficult to determine what constitutes an unusual number of cases of MS. To do this, scientists must: Determine the expected incidence of MS, or number of new expected cases in a given place and time, based on its population at risk in that area. Compare the expected incidence with the reported incidence. Difficulties in Researching Clusters The incidence of MS may not be documented for an area with a reported cluster. Since MS is not infectious, healthcare professionals do not have to report cases to the federal government. Also, the National Neurological Conditions Surveillance System at the Centers for Disease Control and Prevention (CDC) did not begin its work in tracking cases until 2019. This makes it difficult to find the right comparison group with a known incidence of MS. Calculating an expected incidence rate then gets even more complicated. We know that MS rates vary by latitude. The disease also occurs more often in women than men and in people with northern European roots than in others. Therefore, the expected incidence in an area must factor in not only its location, but also the age, gender and ethnic makeup of its population. Also, MS is more common in people who have family members with the disease, which indicates genetic susceptibility, so relationships within a reported cluster must also be considered. Additional reasons that MS clusters are difficult to investigate include: Uncertainty of the diagnosis of MS: Since MS is difficult to diagnose, when people identify an MS cluster, they may actually be including people with similar diseases. Time between onset and diagnosis: Since the first symptoms of MS often occur years before diagnosis, a person diagnosed with MS in an area of a reported cluster may actually have had an earlier onset somewhere else. Coincidence: Clusters may happen by chance, with no common factors that cause MS. Confirming a Cluster of MS A confirmed cluster of MS means that the incidence of definite MS in an area is much higher than expected. However, a very large number of MS cases in a neighborhood or county may turn out to be the expected number. If you have concerns or questions about an MS cluster in your community, talk to your local public health department. Its officials are qualified to investigate suspected clusters. A cluster of multiple sclerosis is the perception of very high number of cases of MS in a particular time and place. MS clusters may signal possible environmental or genetic risk factors that cause or trigger the disease. But so far, cluster studies have not produced clear evidence of any such factors. Investigating Clusters The process of investigating clusters of any disease, especially MS, is complicated. It is difficult to determine what constitutes an unusual number of cases of MS. To do this, scientists must: Determine the expected incidence of MS, or number of new expected cases in a given place and time, based on its population at risk in that area. Compare the expected incidence with the reported incidence. Difficulties in Researching Clusters The incidence of MS may not be documented for an area with a reported cluster. Since MS is not infectious, healthcare professionals do not have to report cases to the federal government. Also, the National Neurological Conditions Surveillance System at the Centers for Disease Control and Prevention (CDC) did not begin its work in tracking cases until 2019. This makes it difficult to find the right comparison group with a known incidence of MS. Calculating an expected incidence rate then gets even more complicated. We know that MS rates vary by latitude. The disease also occurs more often in women than men and in people with northern European roots than in others. Therefore, the expected incidence in an area must factor in not only its location, but also the age, gender and ethnic makeup of its population. Also, MS is more common in people who have family members with the disease, which indicates genetic susceptibility, so relationships within a reported cluster must also be considered. Additional reasons that MS clusters are difficult to investigate include: Uncertainty of the diagnosis of MS: Since MS is difficult to diagnose, when people identify an MS cluster, they may actually be including people with similar diseases. Time between onset and diagnosis: Since the first symptoms of MS often occur years before diagnosis, a person diagnosed with MS in an area of a reported cluster may actually have had an earlier onset somewhere else. Coincidence: Clusters may happen by chance, with no common factors that cause MS. Confirming a Cluster of MS A confirmed cluster of MS means that the incidence of definite MS in an area is much higher than expected. However, a very large number of MS cases in a neighborhood or county may turn out to be the expected number. If you have concerns or questions about an MS cluster in your community, talk to your local public health department. Its officials are qualified to investigate suspected clusters.