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Letter
Are SARS Superspreaders Cloud
Adults?
Stefano Bassetti,*
Werner E. Bischoff,† and Robert J. Sherertz†
*University Hospital Basel, Basel, Switzerland; and †Wake Forest University
School of Medicine, Winston-Salem, North Carolina, USA
Suggested
citation for this article
To the Editor: The primary mode of transmission of severe acute
respiratory syndrome (SARS) appears to be through exposure to respiratory
droplets and direct contact with patients and their contaminated environment.
However, in summarizing their experiences during the SARS outbreaks in
Toronto and Taiwan, McDonald et al. (1) note that certain
persons were very efficient at transmitting SARS coronavirus (SARS-CoV),
and that in certain settings these so-called "superspreaders"
played a crucial role in the epidemic. Airborne transmission by aerosols
may have occurred in many of these cases. The same observation has been
made by others (2–4), but the causes of these superspreading
events and the reasons for the variable communicability of SARS-CoV are
still unclear. Possible explanations include specific host characteristics
(e.g., altered immune status, underlying diseases), higher level of virus
shedding, or environmental factors (1–3).
We hypothesize that superspreading events might be caused by coinfection
with other respiratory viruses. Such a mechanism has been identified in
the transmission of Staphylococcus aureus. Eichenwald et al. (5)
showed that newborns whose noses are colonized with this bacterium disperse
considerable amounts of airborne S. aureus and become highly contagious
(i.e., superspreaders) after infection with a respiratory virus (e.g.,
adenovirus or echovirus). These babies caused explosive S. aureus
outbreaks in nurseries. Because they are literally surrounded by clouds
of bacteria, they were called "cloud babies" (5).
We have shown that the same mechanism also occurs in certain adult nasal
carriers of S. aureus ("cloud adults") (6,7).
Reports indicate that viral infections of the upper respiratory tract
facilitate the transmission of other bacteria, including Streptococcus
pneumoniae, S. pyogenes, Haemophilus influenzae, and
Neisseria meningitidis (8). Moreover, superspreading
events have also been reported in outbreaks of viral diseases such as
Ebola hemorrhagic fever and rubella (3).
Some observations suggest that coinfection with other respiratory viruses
might cause superspreading events with airborne transmission of SARS-CoV.
First, other viral pathogens, including human metapneumovirus, have been
detected together with SARS-CoV in some patients with SARS (4).
Second, few patients with SARS are superspreaders, and upper respiratory
symptoms such as rhinorrhea and sore throat are a relatively uncommon
manifestation of SARS (with prevalences of 14% and 16%, respectively)
(4). Thus, some patients with SARS and upper respiratory
symptoms might be coinfected with other respiratory viruses and become
superspreaders. Interestingly, the report on a SARS superspreading event
in Hong Kong explicitly states that the superspreader had presented with
a "runny nose" (in addition to fever, cough, and malaise) (3).
Therefore, upper respiratory symptoms might be a marker for highly infectious
SARS patients. Future investigations, based upon either existing specimens
from the last outbreak or newly collected specimens from any future outbreak,
should focus on whether an association exits between SARS superspreading
events and coinfection with other respiratory viruses.
References
- McDonald LC, Simor AE, Su IJ, Maloney S, Ofner M,
Chen KT, et al. SARS
in healthcare facilities, Toronto and Taiwan. Emerg Infect Dis.
2004;10:777–81.
- Shen Z, Ning F, Zhou W, He X, Lin C, Chin DP, et al. Superspreading
SARS events, Beijing, 2003. Emerg Infect Dis. 2004;10:256–60.
- Wong T, Lee C, Tam W, Lau JT, Yu T, Lui S, et al. Cluster
of SARS among medical students exposed to single patient, Hong Kong.
Emerg Infect Dis. 2004;10:269–76.
- Peiris JS, Yuen KY, Osterhaus AD, Stöhr K. The
severe acute respiratory syndrome. N Engl J Med. 2003;349:2431–41.
- Eichenwald HF, Kotsevalov O, Fasso LA. The
"cloud baby": an example of bacterial-viral interaction.
Am J Dis Child. 1960;100:161–73.
- Sherertz RJ, Reagan DR, Hampton KD, Robertson KL, Streed SA, Hoen
HM, et al. A
cloud adult: the Staphylococcus aureus-virus interaction revisited.
Ann Intern Med. 1996;124:539–47.
- Bassetti S, Bischoff WE, Walter M, Bassetti-Wyss BA, Mason L, Reboussin
BA, et al. Dispersal of Staphylococcus aureus into the air associated
with a rhinovirus infection. Infect Control Hosp Epidemiol. 2005;26:196–203.
- Sherertz RJ, Bassetti S, Bassetti-Wyss B. "Cloud"
health-care workers. Emerg Infect Dis. 2001;7:241–4.
Suggested citation
for this article:
Bassetti S, Bischoff
WE, Sherertz RJ. Are SARS superspreaders cloud adults [letter]? Emerg
Infect Dis [serial on the Internet]. 2005 Apr [date cited]. Available
from http://www.cdc.gov/ncidod/EID/vol11no04/04-0639.htm
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