Molecular and Source-Specific Profiling of Hospital Staphylococcus aureus Reveal Dominance of Skin Infection and Age-Specific Selections in Pediatrics and Geriatrics.

Staphylococcus aureus  is a major human-associated pathogen that causes a wide range of clinical infections. However, the increased human dynamics and the changing epidemiology of the species have made it imperative to understand the population structure of local ecotypes, their transmission dynamics, and the emergence of new strains. Since the previous methicillin-resistant S. aureus (MRSA) pandemic, there has been a steady increase in global healthcare-associated infections involving cutaneous and soft tissue and resulting in high morbidities and mortalities. Limited data and paucity of high-quality evidence exist for many key clinical questions about the pattern of S. aureus infections. Using clinical, molecular, and epidemiological characterizations of isolates, hospital data on age and infection sites, as well as antibiograms, we have investigated profiles of circulating S. aureus types and infection patterns. We showed that age-specific profiling in both intensive care unit (ICU) and non-ICU revealed highest infection rates (94.7%) in senior-patients > 50 years; most of which were MRSA (81.99%). However, specific distributions of geriatric MRSA and MSSA rates were 46.5% and 4.6% in ICU and 35.48% and 8.065% in non-ICU, respectively. Intriguingly, the age groups 0-20 years showed uniquely similar MRSA patterns in ICU and non-ICU patients (13.9% and 9.7%, respectively) and MSSA in ICU (11.6%). The similar frequencies of both lineages in youth at both settings is consistent with their increased socializations and gathering strongly implying carriage and potential evolutionary replacement of MSSA by MRSA. However, in age groups 20-50 years, MRSA was two-fold higher in non-ICU (35%) than ICU (18.6%). Interestingly, a highly significant association was found between infection-site and age-groups ( p -value 0.000). Skin infections remained higher in all ages; pediatrics 32.14%, adults 56%, and seniors 25% while respiratory infections were lower in pediatrics (14.3%) and adults (17%) while it was highest in seniors (38%). Blood and "other" sites in pediatrics were recorded (28.6%; 25%, respectively), and were slightly lower in adults (18.6%; 8.6%) and seniors (14%; 22.8%), respectively. Furthermore, a significant association existed between infection-site and MRSA (Chi-Square Test, p -value 0.002). Thus, the common cutaneous infections across all age-groups imply that skin is a significant reservoir for endogenous infections; particularly, for geriatrics MRSA. These findings have important clinical implications and in understanding S. aureus profiles and transmission dynamics across different age groups that is necessary for strategic planning in patient management and infection control.