Antimicrobial Resistance (AMR) Surveillance on Stool Culture Specimen in Public Hospitals and Clinics - Hospital Authority AMR Data (2020)

Release date: 13 January 2022

Methodology

Surveillance was conducted following the recommendations of WHO GLASS Manual for Early Implementation (2015) with local adaptation as summarised below:

• Two WHO priority organisms, namely Salmonella species (Salmonella spp.) and Shigella spp. (Shigella spp.) were reported.
• Location of onset would be collectively considered as “Community (undifferentiated)-onset” as a whole instead of adopting the definition by WHO (which defines specimens collected 2 calendar days after hospital admission as hospital-onset) as infections caused by these organisms are mostly community-associated and rarely are hospital-associated.
• For each surveillance period (one calendar year), only the first result would be reported for each patient per specimen type per organism for the same location of onset.
• AST result being “Intermediate” or “Resistant” was considered as “Non-susceptible”, while AST results derived from less than 10 isolates per calendar year were excluded from analysis.
• To avoid misleading or interference by selection bias, percentages of non-susceptibility derived from less than 70% of total isolates were not reported (or remarked to remind readers to interpret with caution.

Since the Action Plan was published in 2017, the situation of 2016 has been chosen as the baseline for comparison.  Fisher’s exact test or chi-square test was used to compare non-susceptibility percentages^[1] between year 2019 and 2020, whereas One-way Cochran-Armitage test was used to look for trend from year 2016 to 2020.  P-value of less than 0.05 was considered as statistically significant.

Results

The total number of patients with stool culture collected increased from about 47,000 in 2016 to about 50,000 in 2019 and then significantly dropped to about 40,000 in 2020.  Majority of the patients with stool culture collected were from those aged 15-64 (40.2% - 46.1%) and aged 65 years or above (35.3% - 40.5%).  The percentage of patients with positive stool culture remained stable over the past years at around 11%.

The overall distribution of the two WHO priority organisms cultured from stool were similar during 2016 to 2020.  The commonest organism isolated from stool in 2020 was Salmonella spp., followed by “other spp.” and Shigella spp. (isolated from 53.2%, 48.5% and 0.3% of patients with positive stool culture respectively).

In general, non-susceptibility on majority of selected antimicrobials for the WHO priority organisms remained stable or showing a decreasing trend from year 2016 to 2020.  However, increasing trends of non-susceptibility percentage were also observed among several pathogen-antimicrobial combinations that may warrant further monitoring.

Salmonella spp.

Comparing between year 2019 and 2020, Salmonella spp. isolates showed no statistically significant change in non-susceptibility percentage towards commonly used antimicrobials. Statistically significant decreasing trend in non-susceptibility percentages from year 2016 to 2020 was observed towards ceftriaxone (7.9%→3.2%). On the contrary, statistically significant increasing trends from year 2016 to 2020 towards ampicillin (59.9%→69.7%) and ciprofloxacin (52.1%→66.7%) were observed.

Shigella spp.^[2],[3]

Comparing between year 2019 and 2020, Shigella spp. isolates showed reduction in non-susceptibility percentage towards ceftriaxone (50.0%→0%) which was statistically significant. Trend analysis revealed statistically significant increasing trend from year 2016 to 2020 towards ciprofloxacin (34.5%→80.0%), while statistically significant decreasing trends were observed for ampicillin (57.6%→26.7%) and co-trimoxazole (81.8%→40.0%).

Trends in non-susceptibility percentages from year 2016 to 2020 with statistical significance mentioned above were summarised in the tables below.

Recommendations

In view of statistically significant increasing trend of non-susceptibility for isolates of Salmonella spp. towards ampicillin and ciprofloxacin and Shigella spp. towards ciprofloxacin, further monitoring would be warranted.  We have alerted working partners of HA about increasing trend of non-susceptibility of the aforesaid antimicrobial-organism combinations for their further investigation and management as appropriate.

Acknowledgement

We would like to acknowledge stakeholders from HA such as Information Technology & Health Informatics Division, Quality and Safety Division, Strategy and Planning Division, and various Working Groups for provision of input to facilitate compilation of findings for year 2020.

^[1]  Non-susceptibility percentage means the proportion of isolates tested for susceptibility of a particular antimicrobial, and with test result being non-susceptible.

^[2]  Data related to ciprofloxacin should be interpreted with caution because CLSI guidelines for sensitivity testing involving fluoroquinolones interpretive criteria for Enterobacteriaceae (except Salmonella spp.) has been updated in 2019. For laboratories that chose to apply the new criteria for reporting in 2019, some Shingella spp. isolates previously categorised as susceptible to ciprofloxacin would be categorised as non-susceptible using the updated zone size requirement under the 2019 criteria.

^[3]  Readers should note only a small number (<50) of Shigella spp. isolates were cultured during the surveillance period, thus the results should be interpreted with caution.