Intestinal Infections by Shigella: Complete ICD-11 Coding Guide

1. Introduction

Intestinal infections caused by Shigella, also known as shigellosis or bacillary dysentery, represent one of the leading causes of invasive bacterial diarrhea worldwide. This acute bacterial disease primarily affects the distal small intestine and colon, causing a characteristic clinical presentation that includes small-volume loose stools, fever, nausea, and frequently more severe symptoms such as toxemia, vomiting, intense abdominal cramping, and tenesmus.

The clinical importance of Shigella infections cannot be underestimated. These gram-negative bacteria of the genus Shigella possess high infectivity, requiring an extremely low infectious dose to cause disease. This means that person-to-person transmission occurs easily, especially in environments with inadequate sanitary conditions, daycare centers, long-term care facilities, and areas with crowded populations.

From a public health perspective, shigellosis represents a significant challenge, particularly in vulnerable populations such as children under five years of age, elderly individuals, and immunocompromised persons. The disease can progress with serious complications, including severe dehydration, seizures, hemolytic-uremic syndrome, and toxic megacolon in rare cases.

Correct coding of Shigella infections is fundamental for multiple purposes: appropriate epidemiological surveillance, proper allocation of public health resources, outbreak monitoring, analysis of antimicrobial resistance patterns, and planning of preventive interventions. Precise identification through the ICD-11 code enables global tracking of this condition and facilitates comparison of data between different health systems, contributing to more effective control and prevention strategies.

2. Correct ICD-11 Code

The ICD-11 code for intestinal infections caused by Shigella is 1A02, classified within the superior category of Bacterial intestinal infections. This specific code should be used when there is laboratory confirmation or strong clinical evidence of infection caused by any species of the genus Shigella.

The official definition establishes that it is an acute bacterial disease involving the distal small intestine and colon, characterized by small-volume softened stools accompanied by fever, nausea, and sometimes toxemia, vomiting, cramping, and tenesmus. This description captures the essential elements of the clinical presentation that differentiates shigellosis from other bacterial intestinal infections.

Code 1A02 encompasses all four main species of Shigella: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. Each species can cause clinical manifestations with varying degrees of severity, with S. dysenteriae type 1 associated with the most severe presentations due to Shiga toxin production, while S. sonnei generally causes milder disease.

The hierarchical structure of ICD-11 positions this code within the system of bacterial intestinal infections, allowing healthcare professionals and coders to quickly identify the specific bacterial nature of the infection. This organization facilitates differentiation from other causes of infectious diarrhea, whether viral, parasitic, or caused by other enteropathogenic bacteria.

3. When to Use This Code

Code 1A02 should be applied in specific clinical situations where there is evidence of Shigella infection. Below, we present detailed practical scenarios:

Scenario 1: Dysenteric diarrhea with laboratory confirmation A patient presents with a three-day history of frequent evacuations with small volume, presence of blood and mucus in stool, fever of 39°C, intense abdominal cramping, and marked tenesmus. Stool culture identifies growth of Shigella flexneri. In this case, code 1A02 is absolutely appropriate, as there is microbiological confirmation of the etiology and the clinical presentation is compatible.

Scenario 2: Outbreak in institution with characteristic symptoms During investigation of an outbreak in a daycare facility, multiple children simultaneously develop fever, bloody diarrhea, abdominal pain, and tenesmus. The first stool culture confirms Shigella sonnei, and subsequent cases with identical clinical presentation can be coded as 1A02, even with pending cultures, due to the clear epidemiological context of person-to-person transmission.

Scenario 3: Typical clinical presentation with suggestive epidemiology Patient returns from travel to an endemic area after consuming food under poor sanitary conditions. Develops watery diarrhea that progresses to dysentery (stools with blood and mucus), fever, nausea, and severe abdominal cramping. Microscopic examination of stool reveals abundant fecal leukocytes. Even before culture confirmation, code 1A02 can be used as a presumptive diagnosis, especially in areas with high prevalence of shigellosis.

Scenario 4: Complication in immunocompromised patient Patient on immunosuppressive therapy develops prolonged bloody diarrhea, persistent fever, and toxemia. Laboratory investigation identifies Shigella dysenteriae. Code 1A02 is appropriate for the primary infection and can be supplemented with additional codes to document the immunosuppressed state and any complications.

Scenario 5: Shigellosis in child with hemolytic-uremic syndrome Three-year-old child with recent history of bloody diarrhea develops pallor, decreased urine output, and laboratory findings compatible with hemolytic-uremic syndrome. Previous stool culture had identified Shiga toxin-producing Shigella dysenteriae type 1. Code 1A02 should be used for the intestinal infection, with an additional code for the hematological complication.

Scenario 6: Convalescent carrier with relapse Patient previously treated for shigellosis returns with a new episode of diarrhea and Shigella isolation on stool culture, indicating relapse or reinfection. Code 1A02 remains appropriate for this new episode of active infection.

4. When NOT to Use This Code

It is fundamental to recognize situations where code 1A02 should not be applied, avoiding coding errors that compromise epidemiological data:

Bloody diarrhea from other etiologies: When investigation identifies other pathogens such as Campylobacter jejuni, Salmonella enterica, enterohemorrhagic Escherichia coli (EHEC), or Entamoeba histolytica, specific codes for these agents should be used. The presence of blood in stool is not exclusive to shigellosis.

Non-infectious inflammatory colitis: Patients with inflammatory bowel disease (Crohn's disease or ulcerative colitis) may present with bloody diarrhea, fever, and cramping, but these conditions require codes completely different from the category of inflammatory bowel diseases, not infections.

Viral gastroenteritis with overlapping symptoms: Although viruses such as norovirus and rotavirus can cause diarrhea, fever, and vomiting, the absence of typical dysenteric features (blood, mucus, tenesmus) and confirmation of viral etiology exclude the use of code 1A02.

Traveler's diarrhea from enterotoxigenic E. coli: Many cases of traveler's diarrhea are caused by enterotoxigenic E. coli (ETEC), which causes profuse watery diarrhea without invasive characteristics. These cases should be coded with 1A03 (Intestinal infections due to Escherichia coli) with appropriate specification.

Asymptomatic carrier: Individuals who shed Shigella in stool but do not present with active clinical symptoms should not be coded with 1A02. There is specific coding for carrier status when clinically relevant.

Post-infectious irritable bowel syndrome: Some patients develop persistent intestinal symptoms after resolution of acute shigellosis. This post-infectious condition requires a different code, related to functional intestinal disorders.

5. Coding Step by Step

Step 1: Assess diagnostic criteria

The diagnosis of shigellosis is based on specific clinical and laboratory criteria. Clinically, seek the characteristic triad: diarrhea (frequently with blood and mucus), fever, and abdominal pain with cramping. Tenesmus (painful sensation of incomplete evacuation) is highly suggestive when present.

Definitive laboratory confirmation requires stool culture with isolation and identification of Shigella spp. Microscopic examination of stool showing abundant fecal leukocytes (positive fecal leukocyte test) supports the diagnosis of invasive bacterial infection. Molecular methods such as PCR can identify specific Shigella genes, offering faster diagnosis.

Epidemiological history is crucial: exposure to confirmed cases, institutional outbreaks, travel to endemic areas, consumption of contaminated food or water, or contact with symptomatic individuals increase the pretest probability.

Step 2: Verify specifiers

Assess the severity of infection: mild cases present with diarrhea without blood and minimal systemic symptoms; moderate cases include dysentery with visible blood, fever, and mild to moderate dehydration; severe cases manifest toxemia, severe dehydration, bacteremia, or complications such as hemolytic-uremic syndrome, seizures, or toxic megacolon.

Document symptom duration, as shigellosis typically evolves over 5-7 days, but may persist for weeks in untreated or complicated cases. Identify whether there are risk factors for severe disease: extreme age, immunosuppression, malnutrition, or comorbidities.

When available, record the identified Shigella species and antimicrobial susceptibility profile, valuable information for epidemiological surveillance and therapeutic decisions.

Step 3: Differentiate from other codes

1A00 - Cholera: Differentiated by profuse watery diarrhea "rice-water stools," without blood or pus, causing rapid and severe dehydration. Cholera is caused by Vibrio cholerae and does not present invasive characteristics such as tenesmus or bloody stools typical of shigellosis.

1A01 - Intestinal infection by other bacteria of the genus Vibrio: Includes infections by Vibrio parahaemolyticus and other non-cholerae species. Generally associated with seafood consumption, they cause watery diarrhea or occasionally dysentery, but microbiological identification of Vibrio (not Shigella) determines the correct code.

1A03 - Intestinal infections by Escherichia coli: Encompasses multiple E. coli pathotypes (ETEC, EHEC, EIEC, EPEC, EAEC). Although enteroinvasive E. coli (EIEC) can cause dysenteric syndrome similar to shigellosis, specific laboratory identification of E. coli versus Shigella determines coding. E. coli O157:H7 (EHEC) can cause hemorrhagic colitis, but generally without high fever, differing from the typical presentation of shigellosis.

Step 4: Required documentation

Prepare complete documentation including: detailed description of symptoms (frequency, stool characteristics, presence of blood/mucus), body temperature and vital signs, physical examination findings (degree of dehydration, abdominal tenderness, presence of tenesmus), laboratory results (fecal leukocytes, stool culture, antibiogram), relevant epidemiological history, instituted treatment, and therapeutic response.

Record complications if present: dehydration with severity grade, bacteremia, hemolytic-uremic syndrome, seizures, rectal prolapse, toxic megacolon, or post-infectious reactive arthritis. This documentation supports coding and allows outcome assessment.

6. Complete Practical Example

Clinical Case

A 28-year-old patient, previously healthy, seeks medical care with a complaint of diarrhea for four days. He reports that initially he presented with watery diarrhea with 6-8 daily bowel movements, accompanied by fever of 38.5°C, nausea, and abdominal cramps. On the second day, the stools became progressively smaller in volume, but with the presence of bright red blood and mucus. He developed an intense sensation of incomplete evacuation (tenesmus) and increased frequency of bowel movements to 10-12 times per day.

Epidemiological history reveals that he works in a daycare where other staff members and children developed a similar condition in the past week. He denies recent travel or consumption of suspicious food outside the work environment.

On physical examination: patient in fair general condition, dehydrated (+/4+), febrile (axillary temperature 38.8°C), heart rate 98 bpm, blood pressure 110/70 mmHg. Abdomen with increased bowel sounds, diffuse pain on palpation, more intense in the left iliac fossa and hypogastrium, without signs of peritoneal irritation. Rectal examination not performed due to intense tenesmus.

Laboratory tests requested: complete blood count showing leukocytosis (14,500/mm³) with left shift; microscopic examination of stool revealing numerous fecal leukocytes and red blood cells; stool culture collected. Patient hydrated orally and empiric antimicrobial treatment initiated with fluoroquinolone.

After 48 hours, laboratory confirms growth of Shigella flexneri on stool culture, sensitive to the prescribed antimicrobial. Patient progresses with progressive improvement of symptoms, reduction of fever and bloody stools. He receives guidance on hygiene, temporary leave from work, and notification of the outbreak to health authorities.

Coding Step by Step

Analysis of criteria: The patient meets clinical criteria for shigellosis with the characteristic triad (dysenteric diarrhea, fever, abdominal pain), presence of tenesmus, and typical progression from watery diarrhea to dysentery. The epidemiological context of an outbreak in a daycare is highly suggestive. Laboratory confirmation with isolation of Shigella flexneri establishes the definitive diagnosis.

Code chosen: 1A02 - Intestinal infections due to Shigella

Complete justification: Code 1A02 is appropriate because there is microbiological confirmation of Shigella flexneri through stool culture, clinical presentation compatible with all defining characteristics (small-volume soft stools, fever, nausea, cramps, and tenesmus), and evidence of person-to-person transmission in an institutional setting. The presence of blood and mucus in the stool, abundant fecal leukocytes, and response to antimicrobial treatment reinforce the diagnosis.

Complementary codes: One may add a code for mild to moderate dehydration if relevant to document severity. In the context of an outbreak, epidemiological codes for exposure may be added as needed. If the patient developed complications such as hemolytic-uremic syndrome, an additional specific code would be necessary.

7. Related Codes and Differentiation

Within the Same Category

1A00: Cholera

When to use vs. 1A02: Use 1A00 when there is confirmation of Vibrio cholerae O1 or O139, with characteristic profuse watery diarrhea "rice-water stools," severe and rapid dehydration, without invasive characteristics.
Main difference: Cholera causes non-invasive secretory diarrhea without blood, pus, or tenesmus, while shigellosis causes invasive diarrhea with destruction of the colonic mucosa, resulting in bloody stools and tenesmus.

1A01: Intestinal infection by other bacteria of the genus Vibrio

When to use vs. 1A02: Apply 1A01 when stool culture identifies Vibrio parahaemolyticus, V. vulnificus or other non-cholerae species, frequently associated with consumption of raw or undercooked seafood.
Main difference: Specific microbiological identification distinguishes these conditions. Non-cholerae Vibrio may cause gastroenteritis, but epidemiology (seafood) and laboratory identification differentiate it from Shigella.

1A03: Intestinal infections by Escherichia coli

When to use vs. 1A02: Use 1A03 when pathogenic E. coli is identified, including ETEC (traveler's diarrhea), EHEC (O157:H7 with hemorrhagic colitis), EIEC (dysenteric syndrome), EPEC or EAEC.
Main difference: Although EIEC causes a syndrome clinically indistinguishable from shigellosis, laboratory identification of E. coli versus Shigella determines the code. EHEC causes hemorrhagic colitis typically without high fever, differing from the febrile presentation of shigellosis.

Differential Diagnoses

Intestinal amebiasis: Entamoeba histolytica can cause dysentery, but generally with more insidious onset, less frequent diarrhea and possibility of hepatic complications (abscess). Differential diagnosis requires parasitological examination of stool with identification of trophozoites or cysts.

Campylobacter colitis: Campylobacter jejuni causes bloody diarrhea and fever, but frequently with more intense abdominal pain, more prolonged course and association with consumption of undercooked poultry. Differentiation requires specific stool culture.

Inflammatory bowel disease: Ulcerative colitis can mimic shigellosis with bloody diarrhea and tenesmus, but presents with a chronic-recurrent course, characteristic endoscopic findings and absence of identifiable infectious agent.

8. Differences with ICD-10

In ICD-10, Shigella infections were coded in category A03, with subdivisions for different species: A03.0 (Shigellosis due to Shigella dysenteriae), A03.1 (Shigellosis due to Shigella flexneri), A03.2 (Shigellosis due to Shigella boydii), A03.3 (Shigellosis due to Shigella sonnei), and A03.9 (Unspecified shigellosis).

ICD-11 simplifies this structure with the single code 1A02 for all Shigella infections, eliminating the need to specify the species in the main code. This change reflects clinical reality where the specific species is often not available at the time of initial coding, and clinical management is similar regardless of species, although severity may vary.

The practical impact of this change includes simplification of the coding process, reduction of errors from incorrect species specification, and greater uniformity in epidemiological data. However, epidemiological surveillance systems should maintain additional fields to record the species when identified, as this information remains valuable for monitoring circulation patterns and antimicrobial resistance.

The alphanumeric structure of ICD-11 (1A02 versus A03 of ICD-10) also facilitates future expansion of the classification system and improves compatibility with digital health information systems.

9. Frequently Asked Questions

How is shigellosis diagnosed? Definitive diagnosis requires stool culture with isolation and identification of Shigella spp. Material should preferably be collected before the start of antimicrobial therapy. Molecular methods such as PCR offer faster and more sensitive diagnosis, identifying specific Shigella genes. Clinically, the combination of diarrhea with blood and mucus, fever, tenesmus, and appropriate epidemiological context strongly suggests the diagnosis. Microscopic examination of stool showing abundant fecal leukocytes indicates invasive bacterial infection, although it is not specific for Shigella.

Is treatment available in public health systems? Yes, shigellosis treatment is widely available in public health systems. The basis of treatment is adequate hydration, which can be oral for mild to moderate cases or intravenous for severe cases. Antimicrobial agents are recommended for moderate to severe cases, reducing symptom duration, bacterial elimination, and transmission. Fluoroquinolones, azithromycin, and third-generation cephalosporins are therapeutic options, although antimicrobial resistance is a growing concern. The choice of antimicrobial agent should consider local resistance patterns and availability in institutional formularies.

How long does treatment last? Antimicrobial treatment of shigellosis typically lasts 3-5 days. Fluoroquinolones such as ciprofloxacin are usually prescribed for 3 days, while azithromycin can be administered as a single dose or for 3 days. Hydration should continue until complete resolution of diarrhea. Without antimicrobial treatment, symptoms generally persist for 5-7 days, but bacterial shedding may continue for weeks. Appropriate treatment significantly reduces symptom duration and the period of transmissibility, being particularly important in individuals who work with food, children in daycare, and healthcare professionals.

Can this code be used in medical certificates? Yes, code 1A02 can and should be used in medical certificates when appropriate. Shigellosis is a condition that justifies absence from professional activities, especially for food handlers, healthcare professionals, and childcare workers, until symptom resolution and, in some contexts, until confirmation of negative stool cultures. The period of absence varies according to case severity and patient occupation, generally between 5-10 days. Proper documentation with the ICD-11 code facilitates administrative processes and justifies the absence to employers and institutions.

Can shigellosis cause serious complications? Yes, although many cases are self-limited, serious complications can occur. Hemolytic-uremic syndrome is the most feared complication, especially with Shigella dysenteriae type 1, causing hemolytic anemia, thrombocytopenia, and acute renal failure. Seizures can occur in children, sometimes preceding diarrhea. Bacteremia is rare but possible, especially in malnourished or immunocompromised patients. Other complications include rectal prolapse (in children with severe tenesmus), toxic megacolon, intestinal perforation, and post-infectious reactive arthritis. Severe dehydration remains the most common and potentially fatal complication if not treated appropriately.

Is there a vaccine against Shigella? Currently there is no licensed vaccine against Shigella available for clinical use, although multiple vaccine candidates are in development and clinical testing phases. The complexity of the immune response necessary for protection, diversity of Shigella species and serotypes, and technical challenges in producing effective vaccines have delayed development. Current prevention is based on hygiene measures: adequate hand washing, basic sanitation, appropriate water treatment, careful food handling, and isolation of cases during the contagious phase.

How to prevent transmission in institutional settings? Prevention of outbreaks in daycare centers, schools, long-term care facilities, and hospitals requires multiple measures. Rigorous hand hygiene with water and soap (preferable to alcohol gel, as Shigella forms biofilms) after using the bathroom and before handling food is fundamental. Confirmed or suspected cases should be excluded until symptom resolution. Contaminated surfaces should be disinfected with chlorinated solutions. Children with diarrhea should not attend swimming pools. Food handlers with shigellosis should be excluded until stool cultures are negative. Continuing education of staff and families about fecal-oral transmission is essential.

What is the difference between shigellosis and other causes of bloody diarrhea? Shigellosis is characterized by high fever, small-volume stools with blood and mucus, pronounced tenesmus, and cramping abdominal pain. Campylobacter causes similar symptoms but often with more intense abdominal pain and a more prolonged course. E. coli O157:H7 causes hemorrhagic colitis typically without high fever and with greater risk of hemolytic-uremic syndrome. Amebiasis has a more insidious onset, more protracted course, and can cause hepatic complications. Inflammatory bowel disease presents a chronic-recurrent course. Specific microbiological identification through stool culture or molecular methods is essential for definitive diagnosis and appropriate treatment.

Keywords: ICD-11 1A02, Shigella infections, shigellosis, bacillary dysentery, bloody diarrhea, bacterial intestinal infections, medical coding, differential diagnosis

External References

This article was prepared based on reliable scientific sources:

References verified on 2026-02-04

Intestinal Infections by Shigella

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