A new study from Radboudumc Amalia Children’s Hospital and UMC Utrecht Wilhelmina Children’s Hospital suggests that a simple saliva test can better assess recurrent respiratory infections in children than the standard blood test. The findings, published in the European Respiratory Journal, indicate that children with lower levels of broadly protective antibodies in their saliva are more likely to suffer from severe infections, including pneumonia.
Saliva vs. Blood: A More Effective and Comfortable Diagnostic Tool for Infections
Between 10 and 15 percent of children experience recurrent respiratory infections, often leading to repeated hospital visits. Doctors rely on blood tests to check for antibody deficiencies, but these tests rarely provide valuable insights.
“This is challenging for pediatricians because we want to help the children,” said Dr. Lilly Verhagen, a pediatric infectious disease specialist and immunologist at Radboud University Medical Center. “We investigated whether we could find out more about the severity of the disease in another way. That would be very valuable in determining which children need more care and when it makes sense to give antibiotics.”
In a study of 100 children with recurrent respiratory infections, researchers found no clear link between antibody levels in the blood and disease severity. However, saliva samples told a different story.
“We observed broadly protective antibodies in saliva that work against various pathogens,” PhD student Mischa Koenen explained. “Children with lower levels of these antibodies had more severe infections. This suggests that these antibodies in saliva strongly indicate disease burden.”
Why Saliva Antibodies Matter
Broadly protective antibodies are present in everyone’s airways and are crucial in defending against respiratory infections. They are even found in the saliva of siblings, parents, and healthy caregivers. The researchers discovered that pre-pandemic saliva samples from children contained antibodies capable of binding to the SARS-CoV-2 virus.
Unlike in saliva, these antibodies are rarely found in the bloodstream. This is because the immune system in the blood is designed for targeted responses. At the same time, the respiratory tract requires a broad range of antibodies to defend against constant exposure to airborne pathogens.
“You inhale various things all day, including many respiratory pathogens, so you need a broad spectrum of antibodies in your airways,” Verhagen said. “In the blood, only a few pathogens enter through the mucosa of the intestines or airways, so a strong, targeted immune response is more beneficial there.”
The Role of Bacteria in Respiratory Infections
In addition to studying antibodies, researchers also examined the respiratory tract microbiome—the balance of healthy and potentially harmful bacteria in the airways. Their findings highlight a strong link between the presence of Haemophilus influenzae and the severity of respiratory infections.
This bacterium, which naturally colonizes the airways, was found in higher abundance in children who frequently became ill during winter. Previous studies have linked Haemophilus influenzae to pneumonia, supporting its role in recurrent infections.
“This helps us assess the amount of care and medication children need and which antibiotic to use, as the current standard does not work optimally against Haemophilus influenza,” Koenen said.
Future Applications: Improved Treatment and Vaccines
Saliva and nasal swab testing could significantly improve how doctors assess and treat children with recurrent respiratory infections. While initial blood tests may still be used, saliva and mucosal tests could replace them in follow-up visits, offering a more child-friendly approach.
Beyond diagnostics, the study also suggests new treatment possibilities. Researchers found that the flu vaccine increased the level of broadly protective antibodies in the saliva of healthy caregivers. This discovery opens the door for future therapies that harness these antibodies to protect children from respiratory infections better.
With these promising findings, saliva testing could soon become a key tool in improving the diagnosis and treatment of childhood respiratory illnesses, reducing the burden on children and healthcare systems.
Reference: Mischa H. Koenen, W.A.A. de Steenhuijsen Piters, Marien I. de Jonge, Jeroen D. Langereis, Stefan Nierkens, Mei Ling J.N. Chu, Roosmarijn van der Woude, Robert P. de Vries, Elisabeth A.M. Sanders, Debby Bogaert, Erhard van der Vries, Marianne Boes, Lilly M. Verhagen. Salivary polyreactive antibodies andHaemophilus influenzaeare associated with respiratory infection severity in young children with recurrent respiratory infections. European Respiratory Journal, 2024.
