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Epidemiologic Notes and Reports Investigation of a Smallpox Rumor -- Mexico

On August 13, 1984, CDC was notified by the Infectious Disease Section, California Department of Health Services, of a possible smallpox case. The Contra Costa County (California) Health Department had received the report from a participant in a multinational seminar in Ixtapa, Mexico. On August 10, the last day of the seminar, the course's organizers had recommended that the 250 attendees consult their physicians on their return home, because a course participant had been diagnosed by a hotel doctor as having smallpox.

A seminar staff person told CDC she had understood the hotel doctor to say that, on August 9, he had diagnosed smallpox, and on August 10, he had clarified his diagnosis to "little pox," a form of chickenpox intermediate in severity between chickenpox and smallpox and not found in the United States. CDC alerted officials at the Pan American Health Organization (PAHO) headquarters in Washington, D.C. PAHO staff and Mexican health authorities investigated the rumor and determined that the hotel doctor reported he had told the seminar organizers that he had diagnosed varicella. Apparently, there was confusion in the use of Spanish terms for chickenpox and smallpox.

The patient, a woman from England, had traveled to Mexico on a flight from London via Los Angeles. Within a few days of arrival, she developed a severe clinical illness with high fever, prostration, and a vesiculo-pustular skin rash. When seen by health officials on August 15, she had recovered, and only scabbed skin lesions remained. A report received by PAHO from Mexican authorities confirmed the diagnosis of chickenpox (varicella) by electron microscopic examination of scabs. PAHO reported to the World Health Organization (WHO), Geneva, Switzerland, that the illness rumored to be smallpox was chickenpox. Adapted from California Morbidity (August 31, 1984) as reported by B Benda, F Wise, Contra Costa County Health Dept, R Roberto, MD, J Chin, MD, State Epidemiologist, California Dept of Health Svcs; Pan American Health Organization, Washington, D.C.; International Health Program Office, CDC.

Editorial Note

Editorial Note: In 1980, the World Health Assembly (resolution WHA33.4) endorsed the recommendation of the Global Commission for the Certification of Smallpox Eradication, which states: "In order to maintain public confidence in the fact of global eradication, it is important that rumors of suspected smallpox, which can be expected to occur in many countries, should be thoroughly investigated. Information should be provided to WHO, if requested, so that it can be made available to the world community."

Between 1979 and 1984, 179 reports of suspected smallpox cases were received by WHO (1,2). All these rumors were investigated and found not to be smallpox. The time required for national health authorities to investigate the cases varied considerably, partly in relation to the apparent seriousness of the rumors. For example, a report from Kenya caused some public concern because the patient, who died 3 days after developing a rash, had been a variolator who used material from smallpox patients to immunize others when smallpox was endemic in Kenya. Prompt investigation and laboratory analysis of specimens collected by Kenyan health officials proved within a week he had chickenpox. A report from sub-Saharan Africa required 9 months of investigation to establish that rumors of smallpox in several countries were false.

The smallpox rumor in Mexico illustrates how rumors can be generated and rapidly spread internationally. Because this case involved a pustular rash illness associated with high fever apparently diagnosed as smallpox by a physician, it was more compelling than other rumors of second- or third-hand stories of reported smallpox cases. Prompt reporting, investigation, and diagnosis of all smallpox rumors are essential to maintain confidence in global eradication.


  1. WHO. Orthopox virus surveillance: post-smallpox eradication policy. Weekly Epidemiological Record 1983;58:149-56.

  2. WHO Smallpox Eradication Unit. Personal communication.

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