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

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: sonalsaxena3@rediffmail.com

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