Methicillin-Resistant & Methicillin Susceptible Staphylococcus (Article Critique Sample)

Critical Article Review
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Critical Article Review
Background
The bacterium Staphylococcus aureus is accountable for a diversity of human infections in both local and life-threatening systemic infections. Methicillin resistant S. aureus (MRSA) emerged in 1961 with the capability to survive adverse environment, and has been considered a nosocomial pathogen until recently when it proved to cause community outbreaks of diseases (1). Comprehending emergence of clones that can cause epidemics, pathogenicity, and virulence of MRSA and methicillin susceptible S. aureus (MSSA) has been the interest of microbiologists in this error of molecular technologies (1).
MRSA can be carried for a long time by both suspecting and non-suspecting healthy carriers. Several investigations established the prevalence of MRSA carriage patterns with the scope of consequent risks of infections, mortality and morbidity, and conversion between carriage patterns. The characterized carriage patterns; colonized and non-colonized, provide knowledge on the prevalence of MRSA and MSSA which is indispensable in planning infection prevention strategies (2). Patients who are colonized with MRSA have been shown to have an increased mortality risk as compared to their counterparts who are not colonized. Although a majority of the population show non carriage pattern and conversion is not a common phenomenon, conversion to carriage pattern predisposes to infection and death (2). Persistent carriage requires long-term care and antibiotic exposure though the outcome is still risky depending on stratification despite the intervention. Active programs for surveillance of patients who are non-colonized, but at risk of conversion are vital to reduce the screening cost incurred currently in health care facilities.
Despite the risks associated with carriage pattern where conversion is of significant concern, there are no threatening risk factors associated with community acquired nasal carriage (3). Colonized and infected patients are investigated systematically to determine their carriage patterns, load and strain relatedness of the identified MRSA, and the sites of carriage which most of the times give positive MRSA results before decolonization (4). It is necessary to investigate the relevance of the number of MRSA and MSSA cultured from different sites of the body, their strain relatedness, time, and carriage pattern of subsequent incidents of morbidity, mortality, and quality of life due to time spent seeking for health care (5). This critical review evaluates a research aiming to establish strain relatedness, the long term carriage patterns, and the incidence of subsequent infections in carriers of MRSA and MSSA.
Article Summary
Introduction
The article “Longitudinal Analysis of Methicillin-Resistant and Methicillin Susceptible Staphylococcus aureus Carriage in Healthy Adolescents” (5) aims to investigate the relatedness of MRSA and MSSA strains, the patterns of long term carriage of bacterium, and to assess the incidence of possible subsequent infections. The participants were 154 grade 10 students in high school, adolescent age group, who were screened eight times in eleven months period to confirm nasal carriage, persistent carriage, incidence of infection, and molecular typing performed on the organism’s isolates for relatedness.
S. aureus is a peculiar bacterium with the ability to adapt for survival in an adverse environment, colonize different sites of the body, and invade the body to cause disease through either toxins or purulent invasions. Some individuals with nasal carriage are at risk of infection with S. aureus. The three main carriage patterns are persistent, which has a high incidence of subsequent infection and reduced staphylococcal antigen immunoglobin, intermittent, persistent, and non-carriage.
Community associated Infections with MRSA are increasing in healthy hosts with soft tissue and skin affected the most. The carriage patterns are changing from the usual MSSA colonization to long term persistent community associated MRSA patterns in healthy individuals. The prevalence of MRSA is high in the pediatric population, people who received antibiotics, in the preceding year, and residents of congested environments, with children who attend day care, in the household. For instance, in Taiwan nasal MRSA carriage was 3.7% and 7.8% in pediatrics and adult population respectively. In order to establish MRSA carriage patterns, strain relatedness was investigated with molecular typing on consecutive isolates while recording the incidences of subsequent infections in healthy individuals, in an 11 month study where MRSA is endemic.
Materials and Methods
The volunteer 10th grade high school students provided informed consent to participate in the study, and permission from relevant authorities in Taiwan obtained. An 11 month longitudinal study design was carried out with standard questionnaires and guided interviews. The hypothesized data, potential factors related to S. aureus colonization; demographics, morbidity, lifestyle, household, and health conditions were digitized, processed and analyzed statistically.
Eight samples of anterior nares’ swabs from each participant were taken over 11 months a monthly sample for the first five months followed by 3 monthly samples for the remaining six months, by two investigators who placed them in medium for transport, Venturi Transystem, to a microbiology laboratory. 7 to 8 and 1 to 6 positive cultures were defined as persistent and intermittent in that order. Active surveillance was performed on the staphylococcal disease by all participants reporting illness, investigating skin lesions, surveying health conditions by phone two weekly, and ill subjects referred to hospital for further investigations, management, and being followed up until resolution of symptoms and signs is confirmed.
The isolates were characterized and identified by molecular typing methods, spa gene, multilocus sequencing, PFGE, PCR technique, SCCmec, and TSGH-17. The genetic relatedness were determined on consecutive isolates; strain pair and molecular typing confirmed indistinguishable strains. Statistical methods compared variables between participants; persistent versus non-carriage, and between different strains; MRSA versus MSSA. Chi-square test, Fisher’s exact test, and two-sample test were used to compare variables. Factors associated with MRSA and MSSA were explored with multiple logistic regressions. SAS software was vital in analyzing data. p value of <0.05 was statistically significant while significant factors of <0.1only from a univariate data comparison were included in the final multivariate analysis model.
Results and Discussion
The study aimed at understanding MRSA carriage pattern, strain relatedness in consecutive isolates, and subsequent infection incidences in healthy individuals. The study found that of 154 participants who completed the study, 72 females and all categorized in 15 classes, 26.2% (323) of total cultures (1232) yielded S. aureus strains comprised of MRSA 3.7% (45) MSSA strains 22.2% (278). Seven genotypes were identified predominantly in MRSA isolates. Epidemiological features were found to relate to carriage patterns of both MRSA and MSSA. A family member working at a health care facility, young children in the household, and visiting a health facility regularly, were independent factors increasing the risk of MRSA carriage, but no risk factor associated with MSSA carriage except female gender, which was a protective factor.
Frequent visits to a health facility were found to increase persistent carriage pattern in individuals identified to be persistent carriers. This was not true with non-carriers. The incidence of persistent carriers was not different between MRSA and MSSA strains. Strain relatedness of MRSA and MSSA consecutive isolates was 100% and 80.5% respectively. MSSA carriers had a lower incidence of carrying indistinguishable as compared to MRSA carriers. Persistent carriers had a high incidence of indistinguishable strains as compared to intermittent carriers. The incidence of subsequent infection was found to be higher in MRSA carriers at 16.6% as compared to MSSA carriers at 1.58% and non-carriers at 2.53%, but the findings were not statistically significant.
The results of the study were in agreed with the early studies which showed that Taiwanese adolescents had intermittent and persistent at 33.8% and 14.9% respectively. Persistent carriers differs from both intermittent carriers and non-carriers in higher bacterial loads, greater incidence of subsequent infection, and lower levels of immunoglobin G and A, a finding that is acceptable. Persistent strains were found to be indistinguishable, a characteristic that is indispensable in eradicating infections by S. aureus. However, the difference was not seen in genotype analysis, which was not expected and can be misleading considering that MRSA carriers were few.
The new ST59 clone of MSRA was encountered in more than 80% of cases, which is in tandem with early studies in molecular epidemiology. However, the original clone in Taiwan, a non-ST59 was also found majorly in intermittent carriers. ST59 had subclones, which were distinguished by molecular studies, to minimize errors of misclassification. In the follow up and clinical surveillance studies, MRSA proved to be capable of colonizing human being quite a long time. In case study is not biased, the behavior of MSRA differs not only due to resistance, but also in interaction with the host.
Risk factors for MRSA colonization were identified which was lacking in early studies. Female gender proved to be protective against MSSA colonization. S. aureus colonization is a risk factor for subsequent infection and follow up for carri...