Differential Diagnosis for a 3-week-old girl with fever, irritability, diarrhea, and bloody stools
- Single most likely diagnosis
- Escherichia coli O157:H7 (B): This is the most likely diagnosis given the patient's symptoms of fever, irritability, diarrhea that has become bloody, and the growth of gram-negative rods in blood and stool cultures after 24 hours. E. coli O157:H7 is a common cause of bloody diarrhea in children, and its presence is often associated with severe illness, including hemolytic uremic syndrome (HUS), which can be life-threatening.
- Other Likely diagnoses
- Salmonella enteritidis (D): Salmonella infections can cause similar symptoms, including fever, diarrhea, and irritability, especially in infants. The presence of gram-negative rods in cultures also supports this possibility, although Salmonella is less commonly associated with bloody stools compared to E. coli O157:H7.
- Campylobacter jejuni (A): Campylobacter is another common cause of diarrhea in children and can cause bloody stools. However, it is less likely in this very young patient and does not as commonly cause systemic symptoms like high fever and irritability in infants as E. coli O157:H7.
- Do Not Miss diagnoses
- Listeria monocytogenes (C): Although less likely given the age and presentation, Listeria monocytogenes can cause severe infections in neonates, including sepsis and meningitis. It is particularly concerning in immunocompromised individuals or those at the extremes of age. Given the potential severity, it's crucial not to miss this diagnosis, even though the symptoms and lab findings are not as typical for Listeria.
- Rare diagnoses
- Shigella sonnei (E): Shigella infections can cause dysentery characterized by bloody diarrhea, but they are less common in infants this young. The epidemiology and clinical presentation make this a less likely option compared to the other pathogens listed, especially given the growth of gram-negative rods and the specific symptoms described.