Postpartum endometritis is the most common obstetric infection (2). It leads to prolonged postpartum hospital stays, thus imposing a considerable strain on healthcare resources. Nevertheless, data regarding the association between distinct risk factors, causative pathogens and the severity of the condition are sparse and not consistent. This research outlines our decade-long practice of obtaining cervical swabs for microbiological assessment in managing postpartum endometritis patients. Our objective was to assess the utility of cervical cultures in diagnosing and treating postpartum endometritis by identifying specific risk factors associated with particular pathogens and evaluating the relationship between these pathogens and the severity of the disease severity. Our cohort included 1069 patients who underwent cervical swab collection for microbiologic cultures following a diagnosis of suspected endometritis. Our cohort represents 1.2% of the total number of deliveries in our institution, which is not different than published rates of postpartum endometritis after vaginal delivery but probably lower than the published rate of endometritis following cesarean deliveries (2, 5, 12).
Endometritis is considered to be a polymicrobial infection (3, 9). Clearly, cervical swabs are prone to vaginal microbiota contamination (3). Nevertheless, even studies in which protected culture methods were used found high prevalence of polymicrobial infections (9).
The fact that most microorganisms isolated in cervical cultures from patients with endometritis are part of the normal genital microbiota, makes the task of identifying the causative pathogen even more challenging. For example, Gibbs et al. compared the endometrial microbiota of 74 postpartum patients with and without clinical endometritis, and found no difference between groups. Although they admitted that their finding cannot exclude ‘superabundance’ of pathogens, they postulated that at least some afebrile postpartum women harbour abundant pathogens in the endometrial cavities (17). In conclusion, a definite laboratory confirmation of the microbiological etiology of endometritis is difficult if not impossible. Conversely, despite limitations, pointing at a distinct microorganism in cervical cultures is a standard procedure in clinical microbiology (16).
In our cohort of cervical cultures, single distinct microorganism positivity rate was 33%. It should be emphasized that this rate represents only the probability of a microbiological identification of a single distinct bacteria rather than its true causal role, or the accuracy of endometritis diagnosis. Moreover, another 8% of cultures (Non-virulent and Candida species groups), are of non-virulent microorganisms, which are not considered to be pathogens associated with endometritis but rather represents vaginal microbiota.
In accordance with previous old studies (4, 18), Escherichia coli was the most common distinct organism in endometritis patients, with similar reported incidence (19). The second most common distinct organism in our study was Streptococcus agalactiae (GBS).
In our analysis, we tried to identify association between specific risk factors and particular pathogens. Both prolonged 2nd stage of labor and prolonged rupture of membranes are well known risk factors of postpartum endometritis (1, 14, 20). We found that Enterobacterales are associated with significantly longer 2nd stage of labor, in comparison with Beta-hemolytic Streptococci. This finding might be related to multiple vaginal examinations (1), leading to disruption of vaginal microbiome and iatrogenic introduction of colonic microorganisms in the genital tract. Similarly, Enterobacterales are associated with significantly longer duration of ROP, and again might reflect the tendency of microorganisms to migrate from the lower gastrointestinal tract to the genital tract and/or to flourish in the genital tract during to iatrogenic interventions.
Lastly, we examined the correlation between these pathogens and the disease's severity. Although there are no specific parameters for disease severity in cases of endometritis, we examined a variety of parameters that are linked to the severity of illness. We found that WBC count is significantly higher in patients with endometritis and isolated Enterobacterales and Beta-hemolytic Streptococci in comparison to cases where no distinct microorganism was isolated. This finding is concordant to previous studies that state that endometritis caused by Beta-hemolytic Streptococcus, especially S. pyogenes (Group A Streptococcus), are associated with significant morbidity and mortality (1, 21). Nevertheless, WBC elevation is sometimes physiologic and not pathological, and might be related to longer duration of labor (21). In addition, we found a higher rate of postpartum clinic visit among patients who had isolated Enterobacterales in comparison to patients with either Beta-hemolytic Streptococcus or no distinct microorganisms. This finding is also consistent with the illness severity among patients whose disease is liked to Enterobacterales.
Beside mild differences between the groups of microorganisms as described above, we did not find any other significant association between particular group of microorganisms and disease severity. It is plausible that such differences exist between specific pathogens, and could have been abundant if we focus on the most virulent species (e.g. S. pyogenes). This assumption correlates with studies that suggested that cervical cultures are needed as part of the assessment of patients with endometritis only for finding the specific cases of such high virulent pathogens (11). We believe that the lack of robust differences in disease severity between the groups of microorganisms isolated from cervical cultures questions the added value of this procedure, which due to its technical limitation and lack of standardization does not necessarily point at the culprit organism. It is worth emphasizing that the adequacy of the antibiotic treatment to the isolated microorganisms was not addressed in this study. Furthermore, we did not asses the contribution of cultures’ results to the clinical management and outcome of newborns to the mothers in our cohort.
The study's principal strength lies in its large sample size, comprising a thorough review of 1069 cervical cultures collected during the puerperium period, yielding a substantial dataset for analyzing endometritis genital microbiology. Covering a period from 2011 to 2021, the study provides a longitudinal outlook, mitigating confounding factors arising from shifts in clinical protocols and laboratory techniques. However, it has limitations: its retrospective nature may compromise data integrity; its single-center context (both clinically- and laboratory- wise) may limit broader applicability. Additionally, the inherent risk of contamination in cervical cultures, the polymicrobial nature of most endometritis infections, and the statistical necessity to aggregate diverse pathogens into categories may have obscured more nuanced differences in pathogen-specific diseases. Moreover, microbiological sampling and processing technics are not standardized locally or globally. For example, the use of speculum, cervical vs. vaginal sampling, swab type, culture media type, etc. are not universal and may have a dramatic effect on the yield and results of the culture. Likewise, anaerobic cultures are not consistent in its methodology in our study and worldwide, thus it is difficult to estimate the true contribution of obligate anaerobes (some are vaginal microbiota) to endometritis cases.
In conclusion, this study presents valuable insights into the role of cervical cultures in diagnosing and managing postpartum endometritis. We analyzed 1069 cervical cultures from a single tertiary referral center, revealing a 33% positivity rate for single distinct microorganism, with Escherichia coli and Streptococcus agalactiae being the most commonly isolated organisms. Although we did find association between few consensual risk factors and measures of disease severity with specific pathogens, the differences between the groups of microorganisms are subtle. The lack of significant differences in disease severity across various microorganism groups raises questions pertaining to the contribution of distinct bacterial identification in endometritis management. Further investigation is needed in order to define whether there is a correlation between the adequacy of antibiotic treatment based on the microorganism’s antibiogram and the maternal clinical outcome, and whether there is any relation between the microorganism to the perinatal outcome.