Outbreak of unexplained illness in a middle school - Washington, April 1994

Morbidity and Mortality Weekly Report, Jan 12, 1996

Editorial Note: MSI is frequently reported as the cause of acute outbreaks of unexplained illness in school settings (1-4). Characteristics of such outbreaks include 1) lack of illness ifi others sharing the same environment; 2) symptoms including headache, nausea, weakness, dizziness, hyperventilation, and fainting; 3) a preponderance of cases among females; 4) "line-of-sight" transmission, and 5) relapse of illness. The outbreak in Washington, although generally consistent with MSI, was uncharacteristic of MSI in ihat it extended throughout a multibuilding facility and the investigation did not detect evidence of hyperventilation or fainting.

The findings in this report are subject to at least three limitations. First, inspection of the facility and sampling was performed 24 hours after onset of the outbreak and, therefore, may have resulted in failure to identify a causative agent that was ventilated out of the facility before sampling began. Second, the retrospective, self-administered survey was conducted after extensive media coverage of the event and probably resulted in an overestimate of the actual number of cases. Third, this investigation did not include examination by a physician to ascertain the presence of physical findings among those reporting illness.

Although school closure, extensive environmental sampling, and epidemiologic investigation may not be routinely indicated after events such as this, responses to such outbreaks should be individualized and should take into account the perceptions of building occupants and perceived health and safety concerns. Whenever possible, the diagnosis of MSI should be communicated to building occupants promptly and openly to prevent recurrence and facilitate reoccupancy.

References

[1.] CDC. Mass sociogenic iliness in a day-care center-Florida. MMWR 1990;39:301-4. [2.] Small GW, Borus JF. Outbreak of iliness in a school chorus. N Engl J Med 1983;308:632-5. [3.] Goh KT. Epidemiologic enquiries into a school outbreak of an unusual illness. int J Epidemiol 1987;16:265-70. [4.] Philen RM, Kilbourne EM, McKinley TW, Parrish RG. Mass sociogenic illness by proxy: parentally reported epidemic in an elementary school. Lancet 1989;1:1372-6.