PREVALENCE OF NASAL CARRIAGE OF METHICILLIN RESISTANT STAPHYLOCOCCI IN HEALTHY POPULATION OF GANGTOK, EAST SIKKIM

JIMSA October-December 2008 Vol. 21 No. 4 191
ORIGINAL
PREVALENCE OF NASAL CARRIAGE OF METHICILLIN RESISTANT
STAPHYLOCOCCI IN HEALTHY POPULATION OF GANGTOK,
EAST SIKKIM
DEVJYOTI MAJUMDAR, ANKUR BARUA, BARNALI PAUL
Department of Microbiology Sikkim Manipal Institute of Medical Sciences 5th mile, Tadong,
Gangtok, Sikkim-737102. India
Abstract : Methicillin Resistant Staphylococcus Aureus (MRSA) strains emerged in the last decade as one of the most important nosocomial
pathogens. MRSA may invade the blood and cause potentially serious complications such as bacteremia, septic shock, and metastatic
infections. MRSA infections have recently been identified in the community. There are few studies regarding carriage state of MRSA in the
community and hence, the Epidemiology of MRSA in the community is little understood. Objectives of the study were to (1) to determine the
prevalence of staphylococcal nasal carriers among healthy adults of Gangtok, East Sikkim. (2) to determine the proportion of Methicillin
Resistant Staphylococcus species isolated from nasal carriers in healthy adults of the community. One Nasal swab from each of a total of 280
apparently healthy individuals belonging to 5 different areas of Sikkim was collected using Simple Random Sampling. The collected data
was tabulated in spreadsheets of Microsoft Excel version Office 2000 and analyzed by Epi Info version windows 2000. 247 of 280 swabs
(88.2%) out of them were found positive for staphylococcus. Among 247 staphylococcus nasal carriers, 129(52.2%) individuals were
positive for S. aureus. Staphylococcal nasal carriage among healthy adults not exposed to hospital environment was found to be high
(88.2%). It was also found that 31(24.0%) nasal swabs were positive for MRSA among those positive for S. aureus. The prevalence of MRSA
in community was thus estimated to be of 11.1%. Majority of MRSA nasal carriers in the community belonged to the age group of 20 and 40
years. Proportion of MRSA nasal carriers was lower in Ranipool (16.2%) but higher in Loomse (38.5%) than in other areas. High carriage
rates in different areas located far away from tertiary care level hospitals reveal that living close to a hospital is not a risk factor for MRSA
or MRCNS colonization. Epidemiological studies including genotyping are required to understand in detail, the dynamics of spread of
MRSA and MRCNS in the community.
Key words: Prevalence, Methicillin Resistant, Staphylococcus aureus, Nasal Carriers, Community
INTRODUCTION
Staphylococcus aureus (S. aureus), a Gram positive coccus,
is frequently found as a part of the normal human microflora.
The organism can be carried asymptomatically for weeks or
months on mucous membranes but only transiently on intact
skin1. Nasal carriers of S. aureus are more prone to skin sepsis
and postoperative staphylococcal infections than non-carriers2.
Studies show that S. aureus techoic acid, which is present in
the surface of S. aureus and coagulase negative staphylococci,
is the primary factor necessary for attachment to nasal
vestibular mucosa3. S. aureus was the most common cause of
nosocomial infections reported in USA during 1990-19964.
Methicillin Resistant Staphylococcus Aureus (MRSA) strains
were initially described in 1961 and emerged in the last decade
as one of the most important nosocomial pathogens5. MRSA
may invade the blood and cause potentially serious
complications such as bacteremia, septic shock, and serious
metastatic infections (endocarditis, pneumonia, osteomyelitis,
and arthritis) 6. Healthcare workers’ hands, the environment,
and airborne transmission (in the case of staphylococcal
pneumonia) are the most common means of spreading MRSA.
Infected and colonized patients provide the primary reservoir
and transmission is mainly through hospital staff 7. Common
factors associated with acquiring MRSA in any acute care
setting include prolonged hospital stay, use of broad spectrum
antibiotics, greater number and longer duration of antibiotic
use, stay in an ICU or burn unit, surgical wounds, decubitus
ulcers, poor functional status and proximity to another patient
with MRSA 8, 9. MRSA is a strain of S. aureus that has
developed resistance to methicillin and other beta ß-lactamaseresistant
penicillins and cephalosporins10. However, MRSA
infections have recently been identified in the community,
which raised a question of whether these infections were
transmitted from hospital, or they were caused by different
resistant strains. The sharp increase in the prevalence of MRSA
acquired infections in many communities had led to the
consideration of outpatients as a source of infection in an
institution11. However, there are few studies regarding carriage
state of MRSA in the community. Majority of the studies, so
far, had been conducted on the patients and staff members of
the hospital6. Epidemiology of MRSA in the community is
little understood or not studied at length. A few reports on
MRSA in the healthy population of Nigeria, USA, Canada,
Pakistan and Japan are available in the world literature. Till
the beginning of study no report on the prevalence of MRSA
in the community in India was available. Case reports of
community acquired MRSA infections had been increasing
since last 3 years in the tertiary care level hospitals in Gangtok
of East Sikkim. Hence, there was an urgent need for evaluation
of nasal carriage of staphylococci and Methicillin resistant
staphylococci. With this background, a study was undertaken
to determine the prevalence of MRSA among healthy subjects
Correspondence: Dr. Ankur Barua, Assistant Professor, Department of Community Medicine, Sikkim – Manipal Institute of Medical
Sciences (SMIMS), 5th Mile Tadong, Gangtok – 737 102 India Fax.: 03592-231496, e-mail : ankurbarua26@yahoo.com
192 JIMSA October-December 2008 Vol. 21 No. 4
in the community in Gangtok of East Sikkim in India.
MATERIALS & METHODS
Background Information: Gangtok with Geographic-locations
of (Lat/Lon Bounding Box: North=27.333332
South=27.333332 East=88.61667 West=88.61667 and altitude
of 1547 m) has a population of 550,000. There are two tertiary
care level hospitals, one government and the other private, at
a distance of 5 miles apart in East Sikkim.
Study Period: Two months (March 2005 - April 2005).
Sample Size: One Nasal swab from each of a total of 280
apparently healthy individuals was collected for the study.
Sampling Technique: Simple Random Sampling by using the
probability proportionate to sample size (PPS) method was
used.
Selection Method: At the beginning, a spot-map of dwellings
of different areas of East Sikkim was prepared. Then each
village and nodal areas were identified in it and numbered
serially. From these numbers, five spots (areas) in the map
were randomly selected through lottery method. Thus, the areas
selected for survey were - Deorali-Daragaon, Metro-point,
Sarswati temple area, Loomse & Ranipool in East Sikkim.
Households in the selected survey areas were numbered serially
and specific number of households in each area (as calculated
by power analysis from software package of epi-info version
windows 2000) was chosen according to PPS method.
Individual households were selected by using the random
number table. Only one individual from each household was
selected for the study through lottery method.
Study Area: Five areas that include Deorali-Daragaon, Metropoint,
Sarswati temple area, Loomse & Ranipool.
Inclusion Criteria: Only one individual was included in the
study from each household. Selection was done through lottery
method after arranging all household members in ascending
order of age.
Exclusion Criteria: Since, Staphylococcus aureus (S. aureus)
was frequently found as a part of the normal human micro
flora, children below 13 years of age were excluded from the
study. Persons who had been admitted in a hospital in the
preceding 12 months or had used any antibiotic during that
period or worked in a health care center were also not included
in this study.
Materials used for the survey: Sterile cotton-swabs, sterile
test tubes, nutrient agar (HiMedia Laboratories Private Ltd.),
Mueller-Hinton agar (HiMedia Laboratories Private Ltd.)
supplemented with 4% NaCl, Oxacillin disk-1ìg (HiMedia
Laboratories Private Ltd.), Control strain NCTC 6571 (ICMR,
Dibrugarh), Other reagents for catalase, oxidase, Coagulase,
phosphates, DNAse and sugar fermentation tests.
Data collection procedure: Nasal swabs were collected by
sterile, dry cotton swabs from anterior nares of each nostril of
a subject, inserting the swab and then gently rotating the swab
three times12. The swabs were immediately placed in test tubes
for further processing in the laboratory. All the isolates were
tested for coagulase production following standard procedures.
Staphylococci spp isolated were tested for Methicillin
resistance by using modified Stokes same plate comparative
disc diffusion method23 using 1ìg Oxacillin disk. Mueller-
Hinton agar with 4% NaCl medium was used to detect
Oxacillin resistance, incubated at 35°C for 24 hours13. Zone
diameter of the test strain was measured in millimeter with a
scale. Strains were classified as resistant or sensitive following
standard procedure.
Data Analysis: The collected data was tabulated in
spreadsheets of Microsoft Excel version Office 2000 and
analyzed by Epi Info version windows 2000.
RESULTS
Nasal swabs from 280 healthy adult subjects were examined
and among them 247(88.2%) were found to be positive for
staphylococcus. Of 247 Staphylococcal nasal carriers,
129(52.2%) were positive for Staphylococcus aureus (nasal
carriers of S. aureus) and the remaining coagulase negative
staphylococci. Out of 129 S. aureus isolates, 31(24%) isolates
were Oxacillin resistant and these are referred as MRSA. The
prevalence of MRSA in community was thus estimated to be
of 11.1%.
Among 247 staphylococcus nasal carriers, 171(69.2%) were
males and 76(30.8%) were females. S. aureus, isolated from
19(21.6%) out of 88 male, and 12(29.3%) from the 41 female
carriers were Methicillin resistant. However, difference in
carriage rates of MRSA among male and female subjects was
statistically not significant [÷2 =1.79, p=0.181(Yates
corrected)].
MRSA nasal carriers in the community were high (26.6%) in
age group of (20-40) years of age and less (10%) in age groups
below 20 years and above 40years. MRSA nasal carriage was
lower in Ranipool (16.2%) and higher in Loomse (38.5%)
than in other areas. But these differences are statistically not
significant [÷2 =1.72, p=0.156 (Fisher exact 2-tailed)].
Out of 247 staphylococcal isolates, 118 (48%) were Coagulase
Negative Staphylococci (nasal carriers of CNS) and among
them, 26(22%) CNS was found to be resistant to oxacillin,
referred to as Methicillin Resistant Coagulase Negative
Staphylococci (MRCNS). Sex-wise break up of nasal carriers
of CNS and MRCNS did not show any significant difference
[÷2=0.04, p= 0.835 (Yates corrected)] in the rates of nasal
carriage among male and female carriers. MRCNS prevalence
was high near the Saraswati temple area (28.6%) of lower
Tadong and Loomse (28.6%). MRCNS nasal carriage rate was
also higher in the age group below 40 years of age (24.75%).
DISCUSSION
S. aureus nasal carriage rates in various populations have been
investigated in the developed countries with temperate
climate14 but no such study among healthy population had been
reported from India so far. Researchers reported that nasal
carriage of S. aureus varied in different communities. The
JIMSA October-December 2008 Vol. 21 No. 4 193
results of the present study showed that nasal carriage of
staphylococci was as high as 88.2% and in 52.2% cases, S.
aureus were isolated. The prevalence of MRSA in the
apparently healthy community of East Sikkim was estimated
to be of 11.1%. A total of 129(46.1%) among 280 healthy
individuals screened were nasal carriers of Saureus. Similar
findings were reported by Anwar et al in their study in Lahore,
Pakistan who screened 1024 and 636 apparently healthy
persons from urban and rural area respectively for nasal
carriage of Staphylococcus aureus and MRSA and reported
that in urban areas prevalence of nasal carriers of S. aureus
was estimated to be 16.99%, but in rural areas, it was 11.32%.
In urban areas prevalence of nasal carriers of MRSA was found
to be 22.98% as against 11.11% in rural areas11. In a study by
Lamikanra et al it was observed that 56.4% of healthy Nigerian
students were nasal carriers of S. aureus14. Tanaka et al, while
studying S. aureus in healthy individuals in Japan reported
24.3% of them to be of nasal carriers15. In a study conducted
at University of Texas, F. Moreno et al reported that 99 (58%)
of 170 isolates of S. aureus were from community cases; the
community to nosocomial case ratio was 2:1; no significant
risk factors differentiated patients with community MRSA
from community MSSA16.
There was no statistically significant difference in the
prevalence of S. aureus nasal carriage between male and female
subjects in the present study. This finding was contrary to that
observed in the study done in Nigerian population where
females harbored S. aureus significantly more often than
males14.
An area-wise analysis of methicillin sensitive vs. resistant
strains of CNS infections showed that statistically there was
no significant difference in nasal carriage rate of MRCNS in
areas near a tertiary care level hospital and away from the
hospital. The reason for much higher rate of MRSA nasal
carriage in Gangtok needs to be further investigated. A
surveillance centre is necessary to be established for
monitoring the problem of MRSA and MRCNS among the
general population in India since Methicillin Resistant strains
are increasing in other parts of the world. It is clear that
epidemiological studies including genotyping are required to
understand in detail, the dynamics of spread of MRSA and
MRCNS in the community. Moreover, acute and recurrent
infections with S. aureus and MARSA are a possibility of
developing drug resistant staphylococcal strains in the
community. As the threat of acquiring multi-drug resistant
staphylococcal infection increases with increasing prevalence
of MRSA in general population, it is recommended that more
studies be carried out in a larger scale in the general population
along with the hospitals in order to keep updated information
on nasal carriage of MRSA.
CONCLUSION
Case reports of community acquired MRSA infections had
been increasing since last 3 years in the tertiary care level
hospitals in Gangtok of East Sikkim. Hence, there was an
urgent need for evaluation of nasal carriage of staphylococci
and Methicillin resistant staphylococci. The prevalence of
MRSA in the apparently healthy community of East Sikkim
was estimated to be of 11.1%. Majority of MRSA nasal carriers
in the community belonged to the age group of 20 and 40 years.
Proportion of MRSA nasal carriers was lower in Ranipool
(16.2%) but higher in Loomse (38.5%) than in other areas.
Staphylococcal nasal carriage among healthy adults, not
exposed to hospital environment, was found to be high (88.2%).
It was found in this study that there was no age / gender /
location specific difference in nasal carriage rate of MRSA or
MRCNS around the tertiary care level hospitals. High rate of
MRSA nasal carriage among healthy adults in general
population needed further investigation. High carriage rates
in different areas located far away from tertiary care level
hospitals reveal that living close to a hospital is not a risk factor
for MRSA or MRCNS colonization. Epidemiological studies
including genotyping are required to understand in detail, the
dynamics of spread of MRSA and MRCNS in the community.
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