Isolation & Quarantine Measures in Response to a Smallpox Emergency

Principles of Isolation

Smallpox Transmission

Smallpox is most often transmitted through direct contact with respiratory droplets. Transmission usually requires close, face-to-face contact. Rarely the disease can be spread through airborne transmission of infectious particles over greater distances, usually associated with cases that have a cough, which is not a usual feature of smallpox.

Although rare, airborne infection over longer distances did sometimes occur. Two hospital outbreaks in Germany seem to have secondary cases arising from airborne spread. In the hospital associated outbreak in Meschede, Germany, a case of smallpox had been confined o his room before being diagnosed with smallpox and transferred to the smallpox hospital. In spite of his isolation, 19 further cases of smallpox occurred on all three floors of the building in which the index case had been housed before transfer to the smallpox hospital. Reasons airborne transmission may have occurred include:

  1. Confined to private room as a suspected typhoid fever case with contact isolation not respiratory isolation.
  2. Smoke studies showed fairly brisk air currents by heating currents within the hospital that may have contributed to the distribution of air from the patient’s room.
  3. The patient had prominent cough.

Today’s infection control practices and hospital ventilation engineering controls are more strict and should prevent transmission by preventing circulation of air from an isolation room to other areas of the hospital if implemented appropriately.

Transmission has occasionally been linked to fomite such as clothing or bedding that has been contaminated by dried respiratory secretions or lesion drainage of cases. Smallpox was rarely transmitted by fomites. Although the vast majority of smallpox cases can be traced back to close, face-to-face contact and not to fomite contact, this study by Downie et al. Demonstrated that live variola virus could be recovered from bedding and clothing used by smallpox patients and therefore could serve as a possible source of infection. Transmission to laundry workers by infected bedding/clothing was reported during several outbreaks by Dixon and others. Wetting down the materials or avoiding sorting prior to washing to prevent re-aerosolization of dried secretions and decreased the risk for this type of transmission.

The environment immediately around the patient (e.g. pillow, bedclothes) had the highest percentage of positive cultures. This would correspond to areas where respiratory droplets would be most likely to settle and where pustule drainage contamination would be the greatest.

Goals of Isolation and Infection Control

The goals of isolation and infection control are:

  1. Protect the community by removing infectious patients from the community environment.
  2. Protect healthcare workers who must come into contact and care for the patient.
  3. Protect other patients in the hospital.

Isolation is used for diseases that are transmitted through casual contact or respiratory transmission. Strict isolation is used for highly infectious agents that may travel long distances through the air or be caught from cutaneous contact with sores or secretions. Strict isolation requires: restriction to a private room with controlled air flow, persons entering the room must wear gowns, gloves, and respirators capable of filtering out micron-level particles.

Surgical masks give no protection for respiratory isolation, which is used for diseases such as tuberculosis that are spread through the inspiration of infected particles, but have only limited spread through contact with wounds or secretions.

Respiratory isolation requires the same precautions as strict isolation, but without the extensive gowning and gloving. Contact isolation is for diseases that spread by direct contact and limited droplet spread. It requires personal protective measures but not a controlled air supply.

Administrative Controls

Many of the administrative infection control practices that are already utilized in current day hospitals can reduce worker exposures and spread within the hospital. If a suspected smallpox case is admitted to a hospital, utilize vaccinated workers (if available) to care for the patient until the diagnosis is established. People presenting to a hospital with a fever and a rash should be placed in respiratory isolation until an airborne infectious etiology is ruled out (as is done when varicella or measles is suspected). Established infection control procedures should be followed when dealing with potentially infectious waste.

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