More patients with pneumonia visited their GP from August 2023 on than in previous years. The rise in cases of pneumonia among children, adolescents and young adults aged 5–25 years is particularly notable. Nose and throat samples from dozens of patients were subjected to laboratory testing since December 2023. These tests showed that multiple viruses and bacteria were very likely to have been responsible for the increase in cases of pneumonia. That means that no single virus or bacteria was the cause. The increase did not lead to a surge in patients who had to be admitted to hospital, and seems to have passed its peak.
The rise in cases of pneumonia among children aged 0–4 years was particularly notable at first. Pneumonia cases involving children aged 5–14 years and adolescents and young adults aged 15–24 years also rose later. To gain better insight into the cause, general practitioners from the GP practices that serve as Nivel monitoring stations took extra nose and throat swabs from patients with pneumonia and sent the samples to RIVM. A total of 132 samples were submitted and examined from October 2023 to January 2024.
igure 1: Number of children, adolescents and young adults with pneumonia per week
Skip chart Number of children, adolescents and young adults with pneumonia and go to datatableFigure 1: Number of children, adolescents and young adults with pneumonia per week (source: NIVEL Netherlands Institute for Health Services Research).
Research in the laboratory
RIVM investigated which respiratory viruses and bacteria that could cause pneumonia were present in the samples taken from nose and throat mucus.
Figure 2. Number of patients with pneumonia
Skip chart Number of patients with pneumonia in various age groups and go to datatableFigure 2. Number of patients with pneumonia from the Nivel monitoring stations at GP practices in various age groups, as tested by RIVM.
Results for children aged 0–4 years
Many of the samples were found to contain multiple viruses and bacteria. RSV was common in the youngest children (0–4 years). This virus is known to cause pneumonia in young children. The Haemophilus influenzae bacteria was also common in this age group. It was also found frequently among patients aged 65 years and older.
Results for children aged 5–14 years and adolescents and young adults aged 15–24 years
The Mycoplasma pneumoniae bacteria was also found frequently among older children, adolescents and young adults in the age groups of 5–14 years and 15–24 years. This is in line with the indications seen in the laboratories, where these bacteria were often detected in the same period. In other European countries and in China, the bacteria was also cited as one of the causes of the increase in pneumonia.
Figure 3. Percentage of patients with pneumonia who tested positi
Skip chart Percentage of patients with pneumonia and go to datatableFigure 3. Percentage of patients with pneumonia who tested positive for one or more bacteria and/or viruses that can cause pneumonia (selection of main viruses and bacteria displayed).
Other sources of information
Other sources of information also show that no single virus or bacteria was responsible for the increase in pneumonia. The increase did not lead to a surge in seriously ill patients who had to be admitted to hospital. However, the Wilhelmina Children’s Hospital (WKZ) in Amsterdam will join forces with some other hospitals and RIVM to conduct long-term research into serious complications in children and adolescents who come to hospital with pneumonia.
Monitoring respiratory infections
The period in which extra samples were collected for the short-term study has come to an end. GPs at the Nivel monitoring stations are no longer sending extra nose and throat samples from patients with pneumonia for more testing. RIVM will continue monitoring which viruses and bacteria are causing respiratory infections in the Netherlands.