Laboratory Studies

Hematology

The total WBC count reveals no consistent findings. A shift to the left (increased number of band cells) in the differential WBC count in a patient with diarrhea suggests bacillary dysentery. Leukopenia or leukemoid reactions are occasionally detected.

In HUS, anemia and thrombocytopenia occur.

Bacteremia is rare, even in severe disease, possibly due to the superficial nature of Shigella infection; the organism rarely penetrates beyond the mucosa.

Blood culture should be obtained in children who appear toxic, very young, severely ill, malnourished, or immunocompromised because of their increased risk of bacteremia.

Stool examination

Isolation of Shigella from feces or rectal swab specimen is diagnostic but lacks specificity. Routine microscopy may reveal sheets of leukocytes on methylene-blue stained stool smear, which is a sensitive test for colitis but not specific for Shigella species.

In approximately 70% of patients with shigellosis, fecal blood or leukocytes (confirming colitis) are detectable in the stool.

Stool culture

A sample for stool culture should be obtained in all suspected cases of shigellosis.

The yield from stool cultures is greatest early in the course of disease. Guidelines for obtaining specimens to improve the yield are as follows:

Process specimens immediately after collection.
If processing is delayed, use a transport medium (eg, buffered glycerol saline).
Collect more than one stool or rectal (not anal) swab and inoculate them promptly on at least 2 different culture media.
Specimens should be plated lightly onto MacConkey, xylose-lysine-deoxycholate, Hektoen enteric, or Salmonella-Shigella, or eosin-methylene blue agars.

If processing is delayed, a rectal-swab sample can be placed in Cary-Blair transport medium or buffered glycerol saline.

After overnight incubation, colorless, nonlactose-fermenting colonies may be tested by means of latex agglutination to establish a preliminary identification of Shigella infection.

Antimicrobial susceptibility tests of all confirmed isolates should be performed by using the agar diffusion technique. The agar and broth-dilution methods are also widely used. The new Epsilometer strip method (E test) is used to accurately determine the minimum inhibitory concentration (MIC).

Despite meticulous care in obtaining and processing specimens from patients infected with Shigella species, approximately 20% may fail to yield Shigella organisms.

Enzyme immunoassay

An enzyme immunoassay for Stx is used to detect S dysenteriae type 1 in the stool.

Rapid techniques

With rapid techniques, gene probes or polymerase chain reaction (PCR) primers are directed toward virulence genes (invasion plasmid locus).

Other testing modalities

Other testing modalities, such as fluorescent antibody test and enzyme-linked DNA probes, are available in research laboratories.

A systematic review and meta-analysis by Tickell et al reported that the sensitivity of dysentery for laboratory-confirmed Shigella infection ranged from 1·9% to 85·9% in the time period between 1977 and 2016, with sensitivity decreasing over time (p=0·04).^[20]

Other Tests

Additional diagnostic tools, such as gene probes and PCR analysis of stool for specific genes such as ipaH, virF, or virA can detect cases not diagnosed by culture but are usually available in research laboratories.^[21]

Treatment & Management

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Media Gallery

This illustration depicts a three-dimensional (3D), computer-generated image of a number of rod-shaped, drug-resistant, Shigella sp. bacteria. The artistic recreation was based upon scanning electron microscopic (SEM) imagery. Note that the exterior of the Shigella bacteria is fimbriated, covered by numerous thin, hair-like projections, imparting a furry appearance. Courtesy of the Centers for Disease Control (CDC)/James Archer.

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Author

Jaya Sureshbabu, MBBS, MRCPCH(UK), MRCPI(Paeds), MRCPS(Glasg), DCH(Glasg) Consultant Neonatologist and Pediatrian, Sree Gokulam Medical College and Research Foundation, India

Disclosure: Nothing to disclose.

Coauthor(s)

Poothirikovil Venugopalan, MBBS, MD, FRCPCH Consultant Pediatrician with Cardiology Expertise, Department of Child Health, Brighton and Sussex University Hospitals, NHS Trust; Honorary Senior Clinical Lecturer, Brighton and Sussex Medical School, UK

Poothirikovil Venugopalan, MBBS, MD, FRCPCH is a member of the following medical societies: British Congenital Cardiac Association, Paediatrician with Cardiology Expertise Special Interest Group, Royal College of Paediatrics and Child Health

Disclosure: Nothing to disclose.

Walid Abuhammour, MD, MBA, CIC, FAAP, FIDSA Professor of Pediatrics, Michigan State University College of Human Medicine; Adjunct Professor, Department of Pediatrics, Hashemite University, Jordan; Head of Pediatric Infectious Diseases, Department of Pediatrics, Al Jalila Children's Hospital, UAE

Walid Abuhammour, MD, MBA, CIC, FAAP, FIDSA is a member of the following medical societies: American Academy of Pediatrics, International Society for Infectious Diseases, International Society for Infectious Diseases, Jordan Medical Association, Jordan Pediatric Society, Michigan Infectious Disease Society, Michigan State Medical Society, National Arab American Medical Association, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Larry I Lutwick, MD, FACP Editor-in-Chief, ID Cases; Moderator, Program for Monitoring Emerging Diseases; Adjunct Professor of Medicine, State University of New York Downstate College of Medicine

Larry I Lutwick, MD, FACP is a member of the following medical societies: American Association for the Advancement of Science, American Association for the Study of Liver Diseases, American College of Physicians, American Federation for Clinical Research, American Society for Microbiology, Infectious Diseases Society of America, Infectious Diseases Society of New York, International Society for Infectious Diseases, New York Academy of Sciences, Veterans Affairs Society of Practitioners in Infectious Diseases

Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD Clinical Professor, Tulane University School of Medicine; Staff Physician, Ochsner Clinic Foundation

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, Southern Medical Association

Disclosure: Nothing to disclose.

Additional Contributors

Glenn Fennelly, MD, MPH Director, Division of Infectious Diseases, Lewis M Fraad Department of Pediatrics, Jacobi Medical Center; Clinical Associate Professor of Pediatrics, Albert Einstein College of Medicine

Glenn Fennelly, MD, MPH is a member of the following medical societies: Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.