Latent Non-typhoidal Salmonella in Macrophages as a Potential Cause of Persistent Appendicitis

Non-typhoidal <i>Salmonella</i> (NTS) infection typically causes gastroenteritis but can sometimes lead to persistent or recurrent abdominal pain due to mesenteric lymphadenitis. Here, we present a rare case of a 10-year-old Japanese boy who experienced persistent abdominal pain caused by appendicitis in addition to mesenteric lymphadenitis due to NTS. Initially, he exhibited symptoms of gastroenteritis, including transient fever, persistent lower abdominal pain, and loose stools. Stool cultures revealed <i>Salmonella</i> O7, leading to treatment with fosfomycin. However, his abdominal pain persisted and was localized to the right lower quadrant. Physical examination suggested appendicitis, which was confirmed by ultrasound and contrast-enhanced CT findings. The patient was treated with ceftriaxone and oral cefditoren pivoxil, which relieved temporary symptoms. However, the abdominal pain recurred and worsened, necessitating an appendectomy 83 days after symptom onset. Laparoscopic examination revealed a swollen, inflamed appendix. Bacterial culture of the appendiceal contents was positive for <i>Salmonella</i> O7. Histopathological examination showed macrophage-reactive hyperplasia in the submucosa of the lamina propria, and transmission electron microscopy identified numerous rod-shaped bacteria within macrophage lysosomes. Similar findings were observed in the mesenteric lymph nodes, indicating the persistence of <i>Salmonella</i> O7 within macrophages. The patient's symptoms resolved rapidly following appendectomy, and stool cultures turned negative for <i>Salmonella</i> O7 one year post-infection. This case suggests that mesenteric lymph nodes may act as a long-term reservoir where macrophages harbor intracellular <i>Salmonella</i>, ultimately leading to persistent appendicitis. Clinicians should consider appendicitis due to NTS​​​​​​​ in patients with prolonged or recurrent abdominal pain following gastroenteritis.