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Methicillin resistant staphylococcus aureusTRANSCRIPT
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Colonization of methicillin-resistant Staphylococcus aureus 279J HEALTH POPUL NUTR 2002 Sep;20(3):279-280 2002 ICDDR,B: Centre for Health and Population ResearchISSN 1606-0997 $ 5.00+0.20
LETTER-TO-THE-EDITOR
Prevalence of Methicillin-resistant Staphylococcusaureus Colonization among Healthcare Workers
and Healthy Community Residents
Sir,
Methicillin-resistant Staphylococcus aureus (MRSA) is
one of the most widespread nosocomial pathogens of
the late 20th century (1). Various hospital-based studies
have described the incidence of MRSA causing such
infections (1,2). Until a few years back, only
nosocomially-acquired isolates showed such resistance,
but, recently, even community-acquired strains have
shown resistance to methicillin (3,4). Increased reporting
of community-acquired MRSA suggests assessment of
the carriage rate of MRSA among healthy individuals in
the community, who have neither been hospitalized nor
have had antibiotic therapy in the recent past. Also,
MRSA being a nosocomial pathogen, it is important to
assess its carriage rates among healthcare workers. It
was with this background that this study was undertaken
in the GTB Hospital over a three-month period in East
Delhi, India.
In total, 317 nasal swabs were taken from healthy
individuals: 200 from parents accompanying children
at the Well Baby Clinic and 117 from adult volunteers
of both the sexes. Persons with history of hospitalization,
undergoing surgery or treatment of any kind, and intake
of antibiotics in the past 12 months were excluded from
the study. The second part of the study was carried out
among healthcare workers in the GTB Hospital. Two
hundred fifty-two healthcare workers from orthopaedics,
surgery and gynaecology operation theatre were screened
for colonization with MRSA.
The nasal swabs were plated on mannitol salt agar
(Difco) and 5% sheep blood agar. The plates were
incubated for 24 hours at 35 C. Colony morphology,
suggestive of S. aureus, was identified by standard
methods (5). Susceptibility testing of MRSA was done
by the agar screening method on Mueller-Hinton agar
(Difco) containing 6 mg/L of oxacillin and 4% sodium
chloride. Plates were inoculated with a bacterial
suspension matched with 0.5 McFarland standard using
spot inoculation. The plates were incubated for exactly
24 hours at 35 C. Drug-free plates were used as growth
control. S. aureus ATCC 38591 was used in each plate
as MRSA control (5,6). Growth of even a single colony
was taken as an indicator of resistance. Antimicrobial
sensitivity was performed for penicillin (10 IU),
amikacin (10 g), erythromycin (15 g), ciprofloxacin(5 g), vancomycin (30 g), clindamycin (2 g), andgentamicin (10 g) using the guidelines of NationalCommittee for Clinical Laboratory Standards for
disc-diffusion susceptibility. The plates were incubated
at 35 C (6).
Of the 317 nasal swabs taken from the healthy
individuals in the community, 94 (29.6%) yielded growth
of S. aureus. Of the 94 isolates, 17 (18.1%) grew on
oxacillin agar. Of the 252 healthcare workers screened,
S. aureus was detected among 112 persons (44.4%), and
MRSA was detected in 28 samples (25%).
The nasal carriage of S. aureus was 29.6% among
the healthy individuals, while it was 44.4% among the
healthcare workers. The colonization rate may range
from 10% to more than 40% in normal adult population
(7). Our figure of 29.6% correlates well within this. The
nasal colonization rate of 44.4% is on the higher side
probably due to nosocomial exposure among the
healthcare workers. Data reported in other studies in
tertiary care centres show a similar incidence (8).
Colonization of MRSA was significant (p
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280 J Health Popul Nutr Sep 2002 Saxena S et al.
showed higher resistance compared to those from the
community.
MRSA strains have been responsible for many
nosocomial outbreaks. Colonized employees often act
as reservoirs for the spread of this organism within
hospital. There have been a number of reports of
community-acquired MRSA from other parts of the
world (3,4,8). However, it is not always clear whether
3. Herold BC, Immergluck LC, Maranan MC,Lauderdale DS, Gaskin PE, Boyle VS et al.Community acquired methicillin resistantStaphylococcus aureus in children with no identifiedpredisposed risk. JAMA 1998;279:593-8.
4. Berman DS, Eisner W, Kreiswirth B. Communityacquired methicillin resistant Staphylococcus aureusinfection. N Engl J Med 1993;329:1896.
5. Baird D. Staphylococcus: cluster forming cocci. In:Collee JG, Fraser AG, Marmion BP, Simmons A,editors. Mackie & McCartney Practical medicalmicrobiology. 14th ed. New York: Livingstone,1996:245-61.
6. National Committee for Clinical LaboratoryStandards. Performance standards for antimicrobialdisc susceptibility test; approved standard M2-46.6th ed. Villanova, PA: National Committee forClinical Laboratory Standards, 1997.
7. Kloos WE. Staphylococcus. In: Collier L, BalowsA, Sussman M, editors. Topley & WilsonsMicrobiology and microbial infections, v. 2. 9th ed.London: Arnold, 1998:577-632.
8. Thomas JC, Bridge J, Waterman S, Vogt J, KilmanL, Hancock G. Transmission and control ofmethicillin resistant Staphylococcus aureus in askilled nursing facility. Infect Control HospEpidemiol 1989;10:106-10.
S. Saxena, R. Goyal, S. Das, M. Mathur,
and V. Talwar
Department of Microbiology
UCMS and GTB Hospital
Shahdara
Delhi 110 095
India
Email: [email protected]
Fax: 0091-11-2290495
these strains have come from the community or are
hospital strains that have spread to the community.
Molecular techniques may help in solving this problem.
Our results indicate the existence of MRSA even among
the healthy population with no recent exposure to
hospital or healthcare workers, although the isolation
rate and antimicrobial resistance among the healthcare
workers were higher. Larger community-based studies
are needed to confirm that transmission occurs more
frequently in community settings.
REFERENCES
1. Thompson RL, Cabezudo I, Wenzel RP.Epidemiology of nosocomial infection caused bymethicillin resistant Staphylococcus aureus. AnnIntern Med 1982;97:309-17.
2. Layton MC, Heirholzer WJ, Patterson JE. Theevolving epidemiology of methicillin resistantStaphylococcus aureus at a university hospital. InfectControl Hosp Epidemiol 1995;16:12-7.
Table 1. Antimicrobial resistance of MRSA isolates
Isolates from
Antimicrobial Community Healthcare(n=17) workers (n=28)
No. % No. %
Penicillin 17 100.0 28 100.0
Amikacin 4 23.5 11 39.2
Clindamycin 6 35.3 13 46.4
Erythromycin 8 47.0 15 53.5
Ciprofloxacin 10 58.8 20 71.4
Gentamicin 7 41.5 21 75.0
Vancomycin 0 0 0 0