We performed a historical cross-sectional study on S. aureus SSTI and found an increase in the proportion of MRSA over a period of 11 years.

The majority of SSTI are caused by S. aureus. In our study, 68% (499/731) of all culture-positive SSTI samples yielded S. aureus as the causative agent, which is consistent with findings from Gabon (75%), Kenya (46%) or Switzerland (65%) [18,19,20].

The overall proportion of MRSA among all S. aureus in our study was 7%, while the proportion ranged from 3–8% between 2009 and 2016, followed by a marked increase to 20% in 2019. In line with this, previous studies conducted between 2008 and 2012 in Lambaréné observed MRSA rates of 6–11% [14, 20]. Similarly, a prospective multi-center study conducted between 2016 and 2018 in Gabon found a rate of 16% MRSA among all S. aureus isolates [15]. While the above studies included isolates from all types of infections, a study conducted in several Sub-Saharan African countries, including Gabon, on the management of S. aureus SSTI detected 6.5% MRSA [16]. In this multicenter study, the rate of MRSA was similar in superficial and deep-seated infections which is divergent to our finding of significantly higher MRSA rates in deep-seated compared to superficial infections.

The observed increase in the rate of MRSA in isolates originating from the surgical ward of the hospital (18%) may be attributed to the fact that MRSA patients are more likely to fail empirical antimicrobial therapy and therefore progress to more severe infections requiring surgical intervention. This is supported by the high proportion of MRSA-associated purulent infections in our study, such as abscesses, that require surgical drainage [16]. Alternatively, it might point toward a nosocomial transmission of MRSA on surgical wards. Such a transmission might be further supported by a lower MRSA prevalence on pediatric wards. However, such a nosocomial source has not been investigated yet. Past studies rather suggest multiple sources for MRSA colonization as indicated by S. aureus protein A (spa)-types (t186, t653, t121, t729) or multilocus sequence types (ST5, ST8, ST88) among five MRSA isolates from health care workers, patients and the general population in Lambaréné, Gabon [21]. Noteworthy, these sequence types are also among the major MRSA lineages in Africa [22]. Further updated genotyping analysis of MRSA in our study setting are warranted to identify potential new sources and transmission chains.

A recent survey conducted among healthcare workers in our study area revealed a lack of knowledge on causes for the emergence of antimicrobial resistance and poor antibiotic stewardship [23]. Irrational prescription habits and easy accessibility to antimicrobials without a prescription might underlie the increase in MRSA shown in our study region.

A peak in the incidence of S. aureus SSTI was observed in 2012, while the proportion of MRSA was very low (Fig. 1). A malaria vaccination trial was conducted at our study site from 2009 to 2013 [24]. During the primary vaccination series and follow-up visits, the participants were seen by a physician which may have increased the chance of detecting SSTI that were previously undetected, thus, affecting sample sizes during this period. However, there was no active screening for SSTIs, and specimens were only collected and sent to the microbiology laboratory if there was clinical evidence of an SSTI. There were two age groups in the study, one comprising infants aged 6–12 weeks and the other comprising young infants aged 5–17 months. This may account for the observed proportion of approximately two-thirds of children among SSTI patients in our study and the median age of 4 years among patients with S. aureus SSTI. However, previous studies in Sub-Saharan Africa have shown that the median age of patients with S. aureus infections, including SSTI, can be as low as 3–4 years [12, 16].

Our study has several limitations. First, since this is a historical cross-sectional study, we exclusively relied on the medical and laboratory records of the patients for whom microbiological testing was requested. Thus, patients who have not undergone microbiological examination could have been missed in our study, possibly underestimating the rate of SSTI in the study area. Due to the limited medical data, the duration of stay, or applied treatment and outcome of the patients was not completely assessed. In addition, we were unable to classify infections according to standard definitions of hospital-acquired, community-acquired, or healthcare-associated infections [25]. The availability of these data would help to elucidate the role of iatrogenic infections, including those associated with healthcare interactions but emerging within the community. Second, we were not able to analyze the genotype of the MRSA isolates regarding the sequence type or clonal complex attribution. Lastly, the inclusion of a single hospital may not be representative of the entire country or Central African region.