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Natural Disaster Microbiology
Agencies facing threats to human health in the wake of events such as
the 2004 tsunami are recognizing new orders of priorities
Bernard Dixon
pidemics of cholera, dysentery, typhoid fever and other waterborne
plagues have long been feared as possible sequelae to natural disasters like
the Burmese cyclone in May. More
recently, heightened dangers from measles and
hepatitis viruses have become apparent in these
situations. Now, another significant problem is
attracting attention—that of polymicrobial infections with multi-resistant organisms heavily
inoculated into the body during trauma. Indeed,
it begins to seem that the “classical” threats
posed by enteric pathogens have been overemphasized, while those coming from other organisms have been underemphasized.
It is still commonplace to read that outbreaks
of waterborne communicable disease in the
wake of a natural disaster may claim more lives
than the event itself. The risk unquestionably
exists. Yet the hard evidence provides a rather
different picture. After conducting a 10-year
review of the literature, Didier Pittet and his
colleagues point out ( J. Hospital Infect. 68:1,
2008) that such infections are not usually the
major cause of mortality of disaster victims.
Deaths occur mainly through trauma. There
were no severe communicable disease outbreaks
in the aftermath of the 2004 tsunami or of
hurricane Katrina in 2005.
As Gretchen Vogel reported in Science (307:
345, 2005), it was a 1990 study by Ronald
Waldman of Columbia University and Michael
Toole, now of the Burnet Institute in Melbourne, Australia, that first highlighted the importance of measles following disruptions to
normal living. They pointed out that the disease
pushed the mortality rate of children in Ethiopian refugee camps up to 60 times its normal
level.
Waldman and Toole’s work encouraged the
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World Health Organization to reassess the most
prudent priorities to be adopted when health
services assist the population of a stricken area
in coping with the threat of communicable diseases. So, when a relief worker rang WHO officials in Aceh, Indonesia, on 8 January, 2005,
two weeks after the tsunami, to report measles
in an affected village, help was immediately
available. By that afternoon, 1,000 people in the
area had been vaccinated.
Didier Pittet, who is based at the University of
Geneva Hospitals, Switzerland, has been working with colleagues there and at two hospitals in
France to build up a picture of the prevalence of
multiresistant microorganisms among survivors
of natural disasters. Their survey, based on an
extensive Medline and PubMed search for papers on infections in disaster victims, focused
principally on the aftermath of the tsunami.
One of the most striking findings was that
pathogens in repatriated patients were often resistant to several antibiotics. “Moreover, contrary to classical orthopaedic infections, where
Staphylococcus aureus is the main pathogen,
Gram-negative rods and extended-spectrum
beta-lactamase (ESBL)-producing bacteria predominated over Gram-positive pathogens in
tsunami victims, according to reports from
Thailand, Germany, Finland, Sweden, Italy,
Australia and Switzerland,” Pittet and his coworkers report.
“Among nine patients transferred to our institution for treatment or multiple fractures, seven
were colonised (methicillin-resistant S. aureus,
ESBL-producing Escherichia coli) or infected
(multi-resistant Acinetobacter baumannii, multiresistant Stenotrophomonas maltophilia, Scedosporium apiospermium, Alcaligenes xyloxidans, Enterococcus faecium, Pseudomonas
aeruginosa, Nocardia africanum, Mycobacte-
rium chelonae) by multi-resistant organisms
causing severe infections such as cerebral abscesses or spondylodiscitis. Almost every unusual microorganism found in clinical specimens proved to be a potentially infective agent.”
The notion that these isolates originated in the
environment is supported by many reports from
other centers. Several have described species of
Aeromonas and Vibrio, clearly related to the
marine environment, in victims of the tsunami
and hurricane Katrina. Also, the incidence of
meliodosis tends to rise after natural disasters,
while victims of events ranging from the Marmara earthquake in Turkey in 1999 to tornadoes in Georgia and Alabama have developed
infections with gram-negative rods.
“Atypical fungal and mycobacterial infections were often reported in polymicrobial infections in immunocompetent patients, whereas a
high incidence is normally encountered only in
transplant recipients,” the Swiss/French group
reports. “Since these fungi are ubiquitous in soil
and water, traumatic inoculation at the disaster
location is presumably the origin, although
some reports suggest that extensive water damage of hospitals could increase the likelihood of
mould contamination.”
As to why many of the posttsunami isolates
were insensitive to several antibiotics, Pittet and
his collaborators point out that soil is known to
be a reservoir for the development of bacterial
resistance to clinically relevant antimicrobials.
“Antibiotic-resistant bacteria have been isolated
from virtually every environment and region,
including South-East Asia, where they are not
part of the normal skin flora.” Another argument for an environmental origin of both the
organisms and their insensitivity to multiple
drugs was the low prevalence of one organism
that certainly is associated with the health care
environment—methicillin-resistant S. aureus—
as compared with gram-negative rods.
The importance of soil as a reservoir of resistance to antimicrobial agents may have been
underlined by recent work by Gautam Dantas
and coworkers at Harvard Medical School,
Boston, Mass., and Harvard University, Cambridge, Mass. In the first systematic study of its
sort, they isolated hundreds of soil bacteria that
were able to thrive on antibiotics as the sole
source of carbon (Science 320:100, 2008). Of
18 antibiotics tested, representing eight major
classes of natural and synthetic origin, 13 to 17
supported the growth of clonal bacteria from
each of 11 diverse soils.
Dantas and his colleagues were surprised to
find that the bacteria subsisting on antimicrobials were phylogenetically highly diverse, many
being related to human pathogens. “Furthermore, each antibiotic-consuming isolate was
resistant to multiple antibiotics at clinically relevant concentrations,” they write. “This phenomenon suggests that this unappreciated reservoir of antibiotic-resistance determinants can
contribute to the increasing levels of multiple
antibiotic resistance in pathogenic bacteria.”
The Swiss/French findings are further components in a still-evolving view of the impact of
natural disasters on the transmission of communicable diseases. On the one hand, the emphasis
is shifting away from a focus on the fear of
water-borne epidemics traditionally thought to
be associated with disasters. We now realize that
these are not inevitable— even, paradoxically,
after large-scale floods. “In the past three decades, epidemics of waterborne illnesses, such as
cholera and shigella dysentery, have been uncommon after floods and naturally disasters,”
write Michael VanRooyen and Jennifer Learning in the New England Journal of Medicine
(352:436, 2005).
“They are quite common, however, in large
displacement centers and refugee camps. Other
common communicable diseases such as acute
respiratory infections and measles result in high
mortality in populations under stress—particularly among children younger than five years of
age—when they are living in large refugee
camp. . .It is not the disaster but the artificial,
crowded communities that serve as a substrate
for the spread of communicable diseases.”
Recognition of a new order of priorities in
dealing with infectious disease threats in the
aftermath of a natural disaster is one thing. But,
as VanRooyen and Learning indicate, the logistics of meeting those challenges are more complex. I wonder, for example, about the feasibility of some of Pittet’s suggestions—that patients
should not share lavatories or meal facilities
with other patients, and should be transported
only in aircraft fitted with high-efficiency particulate air filtration.
Such practicalities aside, the microbiology of
disaster relief is clearly much more soundly
grounded than it was 20 years ago.
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