Shigella causes bloody diarrhea (dysentery) and non-bloody

diarrhea. Rare manifestations of Shigella infection can include urinary tract infection, invasive infection and hemolytic uremic syndrome.Bloodstream infections can occur but are rare.Appropriate antimicrobial therapy will decrease the duration, transmission, and severity of symptoms and should be prescribed based on the severity of illnessor the need to protect close contacts. 2

Confirmation requires phenotypic, biochemical, and serologic identification. Shigella and inactive E. coli (anaerogenic lactose-nonfermenting) strains are frequently difficult to distinguish by routine phenotypic tests. Unfortunately, routine matrix-assisted laser desorption/ionization–time of flight mass spectrometry (MALDI-TOF MS) are unable to reliably differentiate between Shigella species and E. coli .5

Monitoring a Shigella Outbreak in a Pediatric PopulationAshley Formanek, M(ASCP)

Department of Clinical Microbiology, Children’s Mercy Hospitals and Clinics, Kansas City, MO 64108

Contact: akformanek@cmh.edu Introduction Methods and Materials

Results

Conclusion

Acknowledgements

SWACM2015

Shigella is routinely isolated andidentified from routine stoolculture medium including SS and Maconkey agars.Lactose Non-Fermenting and Xylose Non-Fermenting colonies are selected for testing.

Etest

Spread of Shigella is person to person and facilitated by

the fact that ingestion of as few as 10 organisms is

sufficient to produce infection.

Cohorting convalescing children-that is, letting them attend child care but excluding them from interacting with well children, is utilized in some states. Currently, Missouri state regulations require one negative culture obtained 24 hours after diarrhea has ceased and 48 hours after last dose of antibiotic3

Background

Identification

Increasing resistance to ampicillin and trimethoprim-sulfamethoxazole has led physicians to prescribe azithromycin for treatment of shigellosis. Azithromycin is currently recommended by the American Academy of Pediatrics and the Infectious Diseases Society of America for the treatment of multidrug-resistant shigellosis, although azithromycin susceptibility testing guidelines and interpretive criteria are lacking for Shigella sp .2

Shigella on SS agar

The CDC continues to receive new reports of infections with Shigella strains that are not susceptible to ciprofloxacin and/or azithromycin.1 Kansas City is currently experiencing a Shigella sonnei outbreak; we are monitoring the pediatric population numbers. As of Sept. 9th, 2015, The Children’s Mercy Hospital has isolated 75 S. sonnies. The origination of this outbreak was from daycare facilities, but has now spread throughout the community. We have isolated three potentially different strains; all with different antibiograms. Resistant strains (non-susceptible) to azithromycin had been seen in the 2014 S. sonnei outbreak in Missouri. We wanted to monitor the resistance pattern of our most current isolates, including azithromycin. Additionally, azithromycin is our physicians’ first choice for treatment. We attempted to identify any azithromycin non-susceptible isolates.

To identify antibiogram patterns of the strains of Shigella sonnei we have isolated. Furthermore, performing concurrent azithromycin susceptibility testing on a number of S. sonnei isolates to detect any that are non-susceptible.

Goals

The AST results of 75 Shigella sonnei isolates from a Vitek 2 where gathered and analyzed. The reportable antibiotics for our pediatric population were: Ampicillin, Ciprofloxacin, and Trimethoprim/sulfamethoxazole (SXT).In addition, we performed azithromycin Etests on 29 of those isolates.

Out of 75 total specimens: 82% were ampicillin resistant, 52% were SXT resistant, 34% were multidrug resistant; (resistant to both, ampicillin and SXT and are only susceptible to ciprofloxacin)

29 isolates of Shigella sonnei were sub-cultured for fresh growth. After an incubation time of 18-24 hours, isolated colonies were diluted to 0.5 Mcfarland standard in broth. MH plates were then inoculated with the suspension and allowed to dry. Azithromycin Etest strips were subsequently applied and the plates were incubated for 18-24 hours. The plates were then read and interpreted.

Epidemiological cutoff value of Shigella sonnei, tentatively acknowledged but not verified by the CLSI is 16ug/mL

Azithromycin; a Macrolide/azalide, is a bacteriostatic reagent. Inhibition is read at 80%Etest strip MIC Range: 0.016-256ug/mL

1. CDC Health Advisory June 4, 20152.ASM Press; Manual of Clinical Microbiology 10th Edition. pg.6143. CMH internal Shigella Advisory; Dr. Mary Anne Jackson4. CLSI disk diffusion screenings for AZ5. Prasanna D. Khot and Mark A. Fisher Novel approach for differentiating Shigella species and Escherichia coli by matrix-assisted laser desorption ionization-time of flight mass spectrometry. Journal of Clinical Microbiology 2013 Nov;51(11):3711-6. doi: 10.112 8/JCM.01526-13. Epub 2013 Aug 28

• We determined that there are three different Shigella sonnei strains circulating throughout our pediatric population based on our antibiogram.

• Finally, even though we noted the elevated azithromycin MIC values in 45% of our isolates, to date we have not detected any isolates there are azithromycin non-susceptible.

-Note: We concurrently ran the isolates on our MALDI-TOF MS to determine whether any difference in identification patterns amongst the three antibiograms could be detected. From our 29 isolates there were no distinguishing patterns.

We screened 29 isolates for their azithromycin MICs by Etest method. According to the Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing:• Guidelines and clinical interpretive criteria for azithromycin and Shigella do not exist

• Tentative ECOFF MIC values for Shigella flexneri and Shigella sonnei have been noted

• An azithromycin MIC value of above 16 ug/mL is considered non-susceptible4

From our isolates:• 13 out of 29 isolates had an elevated azithromycin MIC of >8ug/mL

• 87% that were resistant to only 1 class antibiotics had an azithromycin MIC of >=12ug/mL

• 27% that were resistant to 2 classes of antibiotics had an azithromycin MIC of >=12ug/mL

Week 1

Week 2

Week 3

Week 4

Week 5

Week 6

Week 7

Week 8

Week 9

Week 10

Week 11

Week 12

Week 13

Week 14

Week 15

0

2

4

6

8

10

12

14

16

18

ISRRSRRSSSSRTotal

Sum of Isolates' Various Antibiotic Pattern by Week (May-September 2015)(Pattern =Amp-Cipro-SXT)

S= SensitiveI = Intermediate

R= Resistant

Resistance to 1 class of antibiotic MIC90= 16 ug/mL

Resistance to 2 classes of antibiotic MIC90= 12 ug/mL