Transmission during Quarantine 55

infection of health care workers is probably related to increased contact with respiratory secretions, contact with patients during a more contagious phase of critical illness, contact with particular patients at increased likelihood of spreading SARS (i.e. superspreaders), or exposure to aerosol-generating patient care procedures (MMWR 52: 433- 6).

In particular, diagnostic and therapeutic procedures inside the hospitals, such as diagnostic sputum induction, bronchoscopy, endotracheal intubation, and airway suction are potent aerosol-generating procedures, and are now being recognized as high-risk activities situations. Other potentially aerosol-generating procedures include BiPAP, during which air might be forced out around the facemask and thereby aerosolize secretions, and HFOV, during which exhaust from the ventilator tubing is more likely to escape without passing through an antibacterial/antiviral filter (MMWR 52: 433-6).

In Canada, a cluster of SARS cases occurred among health care workers despite apparent compliance with recommended infection control precautions. The probable transmission event was an endotracheal intubation of a patient who was in his second week of illness with clinical deterioration and a severe cough (MMWR 52: 433-6).

Another serious outbreak in a public hospital in Hong Kong could have been magnified by the use of a nebulized bronchodilator (albuterol; 0.5 mg through a jet nebulizer, delivered by oxygen at a flow rate of 6 liters per minute, four times daily for a total of seven days), causing atomization of the infected secretions (Lee).

Transmission during Quarantine

There has been at least one report of SARS Co-V transmission during quarantine (WER 22/2003). Three family contacts of a SARS patients became infected during hospital quarantine because strict isolation was not observed. This illustrates the fundamental principle of not "cohorting" suspect cases. Patients diagnosed with SARS may or may not be infected with the SARS virus, but they are at risk of contracting the infection if they are grouped with infected patients.

Kamps and Hoffmann (eds.)

56 Transmission

Transmission after Recovery

How long patients should remain in isolation depends on whether, and to what extent, patients continue to shed virus from the respiratory tract or from feces after overt clinical symptoms have stopped. Currently, at least 14 days of home quarantine are recommended following discharge. There have thus far been no reports of transmission after discharge.

Animal Reservoirs

There is limited data regarding the role of animals in the origin, transmission and reservoir of SARS CoV. Available data suggest that (Field)

Early SARS cases were associated with animal markets

SARS-like viruses were detected in apparently healthy animals in at least 2 wild animal species in one market place

Preliminary experimental studies in pigs and poultry suggest these species are not likely to play a role in the spread of the SARS coronavirus

Several coronaviruses infect multiple host species

Antibody studies in people working in markets show a higher antibody prevalence among market workers in comparison to the general population

Conclusion

The SARS virus is not easily transmissible outside of certain settings. For a major local outbreak to occur there needs to be

an infectious patient, and

a close community or "tribe", i.e., healthcare workers, military populations, travel groups, religious gatherings, or funerals, with close interactions (kissing, hugging).

www.SARSreference.com

References 57

This gives some hope that SARS will not spread in a totally uncontrolled manner in the community.

The "ideal" conditions for efficient transmission of the SARS virus seem to be:

The patient is highly infectious, shedding great quantities of infectious virus

The patient has co-morbidities that mask the symptoms and signs of SARS

The patient is admitted to a hospital with contact to multiple persons because of the diagnostic work-up, possibly including highrisk procedures such as bronchoscopy, endotracheal intubation, use of nebulizers, etc.

References

1.Avendano M, Derkach P, Swan S. Clinical course and management of SARS in healthcare workers in Toronto: a case series. CMAJ 2003; 168. Published online on June 24, 2003. http://www.cmaj.ca/cgi/content/full/168/13/1649

2.CDC. Outbreak of Severe Acute Respiratory Syndrome - Worldwide, 2003. MMWR 2003;52:226-8. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5211a5.htm

3.CDC. Update: Outbreak of Severe Acute Respiratory Syndrome

- Worldwide, 2003. MMWR 2003; 52:241-248. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5212a1.htm

4.CDC. Severe Acute Respiratory Syndrome - Singapore, 2003. MMWR 2003; 52: 405-11. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5218a1.htm

5.CDC. Cluster of severe acute respiratory syndrome cases among protected health care workers – Toronto, April 2003. MMWR 2003; 52: 433-6. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5219a1.htm

6.CDC. Severe Acute Respiratory Syndrome - Taiwan, 2003. MMWR 2003; 52: 461-66. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5220a1.htm

Kamps and Hoffmann (eds.)

58 Transmission

7.CDC. Infection Control Precautions for Aerosol-Generating Procedures on Patients who have Suspected Severe Acute Respiratory Syndrome (SARS). March 20, 2003. http://www.cdc.gov/ncidod/sars/aerosolinfectioncontrol.htm (accessed May 3, 2003).

8.Chan-Yeung M, Yu WC. Outbreak of severe acute respiratory syndrome in Hong Kong Special Administrative Region: case report. BMJ 2003; 326: 850-2. http://bmj.com/cgi/content/full/326/7394/850

9.Cho KO, Hoet AE, Loerch SC, et al. Evaluation of concurrent shedding of bovine coronavirus via the respiratory tract and enteric route in feedlot cattle. Am J Vet Res 2001; 62: 1436-41. http://SARSReference.com/lit.php?id=11560274

10.Donnelly CA, Ghani AC, Leung GM, et al. Epidemiological determinants of spread of causal agent of severe acute respiratory syndrome in Hong Kong. Lancet 2003; 361:1761-6. Published online May 7, 2003. http://image.thelancet.com/extras/03art4453web.pdf

11.Drosten C, Gunther S, Preiser W, et al. Identification of a Novel Coronavirus in Patients with Severe Acute Respiratory Syndrome. N Engl J Med 2003, 348:1967-76. Published online Apr 10, 2003 http://SARSReference.com/lit.php?id=12690091

12.Dwosh HA, Hong H, Austgarden D, Herman S, Schabas R. Identification and containment of an outbreak of SARS in a community hospital. CMAJ 2003; 168. Published online on Apr. 25, 2003. http://SARSReference.com/link.php?id=2

13.Field H. Possible Role of Animals. WHO Global Conference on Severe Acute Respiratory Syndrome (SARS). 17-18 June 2003. Kuala Lumpur. http://SARSReference.com/link.php?id=15

14.Government of Hong Kong Special Administrative Region, Department of Health. Outbreak of Severe Acute Respiratory Syndrome (SARS) at Amoy Gardens, Kowloon Bay, Hong Kong. http://www.info.gov.hk/info/ap/pdf/amoy_e.pdf (accessed April 30).

15.Hon KL, Leung CW, Cheng WT, et al. Clinical presentations and outcome of severe acute respiratory syndrome in children.

www.SARSreference.com

References 59

Lancet 2003, 361:1701-3. Published online April 29, 2003. http://image.thelancet.com/extras/03let4127web.pdf

16.Hsu LY, Lee CC, Green JA, et al. Severe acute respiratory syndrome (SARS) in Singapore: clinical features of index patient and initial contacts. Emerg Infect Dis 2003; 9: 713-7. http://www.cdc.gov/ncidod/EID/vol9no6/03-0264.htm

17.Lee N, Hui D, Wu A, et al. A Major Outbreak of Severe Acute Respiratory Syndrome in Hong Kong. N Engl J Med 2003; 348:1986-94. http://SARSReference.com/lit.php?id=12682352

18.Li T, Buckley TA, Yap F, Sung J, Joynt GM. Severe acute respiratory syndrome (SARS): infection control. Lancet 2003; 361. http://SARSReference.com/link.php?id=6

19.Peiris JS, Lai ST, Poon LL, et al. Coronavirus as a possible cause of severe acute respiratory syndrome. Lancet 2003, 361:1319-25. Published online Apr 8, 2003. http://image.thelancet.com/extras/03art3477web.pdf

20.Peiris JS, Chu CM, Cheng VC, et al. Clinical progression and viral load in a community outbreak of coronavirus-associated SARS pneumonia: a prospective study. Lancet 2003b; 361:176772. Published online May 9, 2003. http://image.thelancet.com/extras/03art4432web.pdf

21.Poutanen SM, Low DE, Henry B, Finkelstein S, et al. Identification of Severe Acute Respiratory Syndrome in Canada. N Engl J Med 2003, 348:1995-2005. http://SARSReference.com/lit.php?id=12671061

22.Riley S, Fraser C, Donnelly CA, et al. Transmission Dynamics of the Etiological Agent of SARS in Hong Kong: Impact of Public Health Interventions. Science 2003; 300: 1961-6. Published online May 23, 2003. http://www.sciencemag.org/cgi/content/full/300/5627/1961

23.Seto WH, Tsang D, Yung R, et al. Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS). Lancet 2003; 361: 1519–20. http://SARSReference.com/link.php?id=1

24.So L, Lau A, Yam L, et al. Development of a standard treatment protocol for severe acute respiratory syndrome. Lancet 2003; 361: 1615-6.

Kamps and Hoffmann (eds.)

60 Transmission

25.WHO. First data on stability and resistance of SARS coronavirus compiled by members of WHO laboratory network. May 4, 2003. http://SARSReference.com/link.php?id=5 (accessed May 4).

26.WHO. Update 53 - Situation in Singapore and Hong Kong, interpretation of "areas with recent local transmission". May 12, 2003. http://www.who.int/csr/don/2003_04_09/en/

www.SARSreference.com