Rare Paenibacillus Infection Causes Meningitis in Infants: Emerging US Threat

Clinicians should be aware of a rare but potentially fatal infection caused by Paenibacillus dendritiformis, particularly in young infants, according to recent reports. Two cases in the United States, one of which proved fatal, have highlighted the severity of this emerging threat.

The cases, detailed in a Public Health Alert and published in NEJM Records, involved infants from Pennsylvania and Minnesota. Both infants were born prematurely and required care in a neonatal intensive care unit (NICU). Dr. Jessica Ericson, of Penn State College of Medicine and colleagues reported the findings, emphasizing the need for heightened awareness among pediatricians.

“This could be an emerging infection that could become more common,” Dr. Ericson stated. “So, pediatricians who take care of young babies, if they see this kind of infection, they should realize This represents a possibility.”

What distinguishes Paenibacillus infections from other causes of meningitis is the extent of brain damage they can inflict. Dr. Ericson noted that the infection “eats away so much of the brain.”

Paenibacillus species are commonly found in the soil and are spore-forming, gram-positive bacteria. While the exact modes of transmission remain unclear, observations suggest potential links to NICU admissions and, in some cases, maternal drug use. Interestingly, cases in Uganda have been correlated with rainfall and proximity to large bodies of water.

Although considered “exceptionally rare” in the U.S., the true incidence of Paenibacillus infections is currently unknown. Dr. Ericson explained that incidence likely varies geographically. Research in Uganda has indicated that approximately 6% of infants under one month of age presenting with infection symptoms tested positive for Paenibacillus. However, she also suggested that improved diagnostic technologies may be leading to increased detection, rather than a true rise in infection rates. “So, we don’t really know if it’s more common or if we’re just finding it more,” she said.

Treatment of Paenibacillus infections requires prolonged antibiotic courses, often longer than those typically used for meningitis. Clinicians should exercise caution when using narrow-spectrum beta-lactams, as bacterial isolates from the recent U.S. Cases exhibited multiple beta-lactamase genes. Cases in Uganda have demonstrated vancomycin-resistant genes, although U.S. Strains have currently shown susceptibility to vancomycin, they also carry the genetic markers for resistance.

While the optimal antibiotic therapy remains undefined, current evidence suggests that meropenem, combined with thiamine supplementation, may yield the best outcomes. Both P. Thiaminolyticus and P. Dendritiformis produce thiaminase, an enzyme that breaks down thiamine. Early thiamine supplementation may help counteract this effect. The significant brain destruction observed in these cases may be attributable to both the infection itself and the depletion of thiamine in brain tissue.

The Pennsylvania infant, born at 26 weeks’ gestation in February 2025, developed respiratory distress and seizures two months after birth. Her initial NICU stay was uncomplicated, and she had not undergone any neurological procedures. Blood and cerebrospinal fluid (CSF) cultures identified P. Thiaminolyticus as the sole pathogen. A ventriculoperitoneal shunt was subsequently placed to address progressive hydrocephalus, encephalomalacia, and abscesses.

Treatment included eight weeks of continuous-infusion meropenem, with vancomycin and rifampin added due to CSF abnormalities. Thiamine supplementation was initiated four days after symptom onset. At eight months of age, the infant demonstrated eye contact, smiled, and did not exhibit seizures, although she was unable to eat independently, sit unsupported, or roll over.

The Minnesota infant, born at 33 weeks’ gestation, had a stable course following a 22-day NICU stay and 15 days at home. He was readmitted with unresponsiveness and poor feeding. P. Thiaminolyticus was identified as the only pathogen in blood and CSF cultures. Brain imaging revealed “liquefactive meningoencephalitis.”

The infant received 21 days of intravenous ampicillin and underwent placement of a ventriculoperitoneal shunt. However, he developed seizures and feeding difficulties and ultimately died at 11 months of age.

These cases underscore the importance of considering Paenibacillus dendritiformis and Paenibacillus thiaminolyticus in the differential diagnosis of meningitis in young infants, particularly those with a history of prematurity or NICU admission. Further research is needed to fully understand the epidemiology, transmission, and optimal treatment strategies for these potentially devastating infections.