A 5-year-old boy is brought to the emergency department with a 12-hour history of sudden-onset vomiting, abdominal cramps, and watery diarrhea. A parent reports that symptoms began shortly after a birthday party where the child ate potato salad and cream-filled pastries. Temperature is 37.0 C (98.6 F), blood pressure is 115/70 mm Hg, heart rate is 90 beats per minute, respiratory rate is 16 breaths per minute, and oxygen saturation is 98% on room air. On examination, the child appears fatigued with tacky mucous membranes and capillary refill of < 2 seconds. Laboratory results are shown below. Which of the following is the best next step in management? Laboratory Value Result Reference Range White b lood c ell (WBC) c ount 8,500/µL 5,100-13,400 /µL Hemoglobin 13.2 g/dL 1 1.5-13.5 g/dL Platelet c ount 290,000/µL 150,000-450,000 /µL Sodium 138 mEq /L 138 - 145 m Eq /L Potassium 4.1 mEq /L 4.1 -5.8 mEq /L Blood u rea n itrogen (BUN) 12 mg/dL 5-17 mg/dL Fecal lactoferrin Negative Negative Stool m icroscopy Gram-positive cocci in clusters Negative for pathogens

Most cases of acute infectious gastroenteritis are caused by either viral or bacterial pathogens. Now, if a pediatric patient presents with a chief concern suggesting acute infectious gastroenteritis, first perform an ABCDE assessment to determine if they are unstable or stable.

Unstable Patient 0:32–1:12

If unstable, stabilize their airway, breathing, and circulation. Obtain IV access, start IV fluids, and consider administering a fluid bolus.

Next, begin continuous vital sign monitoring, including heart rate, respiratory rate, blood pressure, and pulse oximetry; provide supplemental oxygen if needed; and consider starting antibiotics.

Now that we’ve discussed unstable patients, let’s return to the ABCDE assessment and take a look at stable patients. Start by obtaining a focused history and physical examination.

Stable Patient 1:12–2:30

History typically includes the acute onset of diarrhea, vomiting, anorexia, and abdominal cramps lasting 2 weeks or less.

Some patients also report a fever or a sick contact. Physical exam may demonstrate abdominal tenderness and hyperactive bowel sounds, but in more severe cases, you might see signs of dehydration, like decreased skin turgor, sunken eyes, and dry mucous membranes.

These findings are highly suggestive of acute infectious gastroenteritis. Next, assess whether there are indications for obtaining a stool culture.

These include outbreaks in a childcare setting or school; exposure to animals or contaminated food; blood or mucus in the stool; or recent foreign travel.

Additionally, any young or immunocompromised patient with a high fever should have stool sent for culture. Now, if there’s no indication for a stool culture, you should suspect viral gastroenteritis, which is commonly caused by rotavirus, norovirus, or adenovirus.

Viral Infection 2:30–2:41

Let’s start with rotavirus infection. Affected patients are typically under 18 months of age and unvaccinated, with most infections occurring in the winter months.

Rotavirus 2:41–3:21

Caregivers typically report a sudden onset of fever and vomiting, followed by watery diarrhea one or two days later. With these findings, suspect rotavirus infection.

This is usually a clinical diagnosis, but if needed, you can obtain a stool rotavirus antigen test. A positive test confirms a diagnosis of rotavirus infection.

Now let’s take a look at norovirus infection. History usually reveals a sudden onset of vomiting, followed by watery diarrhea and abdominal cramps.

Norovirus 3:21–4:03

Your patient may also report fever, myalgia, fatigue, and headache. At this point, suspect norovirus infection, which is often a clinical diagnosis.

However, norovirus often causes gastroenteritis outbreaks in closed environments, so if your patient attends a school or daycare, consider further testing, like a PCR stool test.

A positive PCR confirms a diagnosis of norovirus infection. Finally, let’s discuss adenovirus infection.

History commonly reveals low-grade fever and respiratory symptoms, like congestion, runny nose, sore throat, and cough. Patients often have watery diarrhea lasting 1 or 2 weeks, along with vomiting and abdominal pain.

Adenovirus 4:03–4:47

The exam might reveal conjunctivitis. With these findings, suspect an adenovirus infection, which doesn’t usually require laboratory confirmation, but if the diagnosis is unclear, consider obtaining a PCR stool test.

A positive PCR confirms a diagnosis of adenovirus infection. Viral gastroenteritis is usually self-limited, and management consists of supportive care, including oral rehydration solution, possibly in combination with antiemetics.

Supportive Care 4:47–5:01

Alright, let’s switch gears and take a look at patients with one or more indications for a stool culture, starting with noninflammatory diarrhea.

Bacterial Infection 5:01–5:23

In this case, suspect bacterial gastroenteritis. To identify the pathogen, obtain a stool culture with a microscopic exam, and assess the stool for fecal leukocytes.

Now, if fecal leukocytes are absent, your patient has noninflammatory diarrhea. In this case, illness is often caused by toxin-producing bacteria such as Bacillus cereus, Staphylococcus aureus, or enterohemorrhagic E.

Noninflammatory Diarrhea 5:23–5:40

coli. Let’s start with Bacillus cereus infection.

Bacillus cereus 5:40–6:09

The history typically reveals profuse watery diarrhea with abdominal pain, cramps, and less than 24 hours of nausea and vomiting.

Patients might report eating leftover rice that’s been left at room temperature for more than a couple of hours, which is a well-known source of this bacterium.

If the stool culture grows Bacillus cereus, you can confirm the diagnosis. Moving on to Staphylococcus aureus infection.

Staph aureus 6:09–6:37

Patients often report a sudden onset of vomiting, abdominal cramps, and diarrhea. Ingestion of mayonnaise-containing food like potato salad is often the source of Staph.

aureus infection, especially if it was left in a warm environment, such as an outdoor picnic. A positive stool culture confirms the diagnosis of Staphylococcus aureus infection.

Finally, let’s focus on enterohemorrhagic E. coli, or EHEC for short.

EHEC 6:37–7:40

The history typically reveals watery diarrhea and abdominal cramps and followed by bloody stools and vomiting. Symptoms may have started after your patient ate an undercooked hamburger.

If the stool culture is positive for enterohemorrhagic E. coli, diagnose EHEC infection.

Here’s a clinical pearl! E.

coli O157:H7 is a Shiga toxin-producing E. coli, or STEC for short, that’s associated with hemolytic uremic syndrome.

Shiga toxin injures the intestinal epithelium and underlying blood vessels causing inflammation and leading to the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury.

A standard culture won’t identify this strain, so ask the lab to test for it specifically! Now, regardless of its cause, noninflammatory diarrhea is usually self-limited and doesn’t require antibiotics, so supportive care is the mainstay of treatment.

Supportive Care 7:40–7:59

This includes oral rehydration solution, possibly in combination with antiemetics. Alright, let’s switch gears and discuss cases in which fecal leukocytes are present, then starting with diarrhea that contains blood or mucus.

Inflammatory Diarrhea7:59–8:29

This finding indicates the pathogen has caused tissue damage and inflammatory diarrhea. You can narrow your differential further by assessing the stool characteristics.

Let's start with diarrhea that contains blood or mucus. Here, consider infections with Shigella, Campylobacter, and Yersinia.

First up is Shigella infection. Patients typically have a prodrome of fever, chills, nausea, and vomiting, followed by abdominal cramps and small, frequent stools.

Shigella 8:29–9:13

Keep in mind that Shigella can cause seizures in children, and patients may spend time in a daycare setting, where Shigella often causes outbreaks.

A positive stool culture confirms Shigella infection. You can treat Shigella with a third-generation cephalosporin, or azithromycin if your patient is immunocompromised; if they’re experiencing severe illness; or if there’s a public health concern, such as a daycare outbreak.

Next, let’s discuss Campylobacter infection. The history typically reveals fever, with abdominal cramps and pain.

Campylobacter 9:13–9:54

Infection commonly occurs during the spring or summer months, and patients may recall eating undercooked poultry or raw dairy.

If the stool culture grows Campylobacter jejuni, diagnose Campylobacter infection. Remember to culture on selective media, since Campylobacter doesn’t grow well on a standard culture!

Consider prescribing azithromycin if your patient is immunocompromised or if they have a prolonged or severe course of illness.

Last up is Yersinia infection. Patients typically present with fever, in the winter, and history may reveal ingestion of undercooked pork.

Yersinia 9:54–10:45

These patients often experience fever and right-sided abdominal pain, which can mimic appendicitis if tenderness is localized to the right lower quadrant at McBurney point.

This is known as pseudoappendicitis, and Yersinia is the most common culprit. If the stool culture is positive for Yersinia enterocolitica, diagnose Yersinia infection.

This illness is generally self-limited, but you can consider treating with trimethoprim-sulfamethoxazole if your patient is under three months of age; immunocompromised; or experiencing severe illness.

If you prescribe antibiotics, be sure to tailor them to culture results, and provide your patient with supportive care. This includes oral rehydration solution, possibly in combination with antiemetics.

Tailor abx / Supportive Care 10:45–12:02

Now here’s a clinical pearl to keep in mind! If your patient gastroenteritis symptoms report recent antibiotic use or hospitalization, suspect a Clostridioides difficile, or C.

diff. infection.

Antibiotics can alter the intestinal flora without affecting Clostridioides difficile, which allows it to multiply and produce toxins that attack the colon wall.

This causes severe inflammation with pseudomembrane formation at the site of mucosal injury, which is called pseudomembranous colitis.

To test for C. diff., order stool tests for glutamate dehydrogenase antigen and C.

diff. toxins A and B.

You can also order a nucleic acid amplification test to confirm the result. To treat C.

diff. infection, discontinue any current antibiotics and treat with antibiotics like vancomycin and fidaxomicin or metronidazole.

Okay, let’s switch gears and discuss diarrhea with watery stools. In this case, consider infections caused by Vibrio, nontyphoidal Salmonella, and enterotoxigenic E.

Watery 12:02–12:17

coli. First is Vibrio infection.

Patients report sudden onset of fever, vomiting, and profuse watery diarrhea containing mucus and epithelial cells, sometimes referred to as “rice water” stools.

Vibrio 12:17–12:58

Since Vibrio is found in marine environments, your patient might have recently eaten raw oysters or shellfish. If the stool culture grows a Vibrio species, like Vibrio parahaemolyticus or Vibrio vulnificus, diagnose Vibrio infection.

As for treatment, you should consider doxycycline for patients with severe disease. Next, let’s take a look at nontyphoidal Salmonella infection.

Salmonella 12:58–13:55

Patients typically report a sudden onset of fever, diarrhea, and abdominal cramps during the summer or fall months. They may also report a recent exposure to contaminated food, like chicken, eggs, or fresh produce; or to live poultry or reptiles, especially turtles.

Physical exam typically reveals abdominal tenderness. If a stool culture is positive for nontyphoidal Salmonella, confirm a diagnosis of Salmonella infection.

Since antibiotics can prolong Salmonella shedding in stool, reserve them for patients with immunocompromised children; severe disease; or infants under three months of age.

In these cases, treat your patient with third-generation cephalosporins or azithromycin. Finally, let’s discuss enterotoxigenic E.

ETEC 13:55–14:33

coli, or ETEC for short. These patients might report recent travel and usually have non-specific symptoms, like abdominal pain, nausea, vomiting, and diarrhea, possibly in combination with low-grade fever.

If the stool culture grows ETEC, diagnose ETEC infection, which is commonly known as traveler’s diarrhea. Most infections are self-limited, and antibiotics aren’t usually necessary, but you can consider prescribing azithromycin.

Lastly, if you prescribe antibiotics, be sure to tailor them to culture results, and provide your patient with supportive care.

Tailor abx / Supportive Care 14:33–15:14

This includes oral rehydration solution and possibly antiemetics. Here’s one final clinical pearl!

Keep an eye out for post-infectious complications of acute bacterial gastroenteritis. For example, Yersinia, Campylobacter, Salmonella, and Shigella infections are associated with reactive arthritis and erythema nodosum, while Campylobacter infection can be complicated by Guillain-Barre syndrome and IgA nephropathy.

Alright, as a quick recap… Acute infectious gastroenteritis refers to an infection of the stomach and intestines that has a rapid onset and lasts 2 weeks or less.