Nasopharyngeal cultures in children; when, what and why?

Introduction: Nasopharyngeal cultures are commonly used to determine the causative bacteria in upper airway infections. However, several bacteria can occupy the nasopharynx simultaneously and most healthy children are asymptomatic carriers of presumptive pathogens. This makes the interpretation of nasopharyngeal cultures difficult. Knowledge about which bacteria reside in the nasopharynx can assist the physician in the choice of antibiotic treatment and might also predict the risk of complications. Today, little is known about how nasopharyngeal cultures are being used in clinical practice.

Objectives: The aim of this study was to explore how nasopharyngeal cultures are used in clinical practice, when and why they are performed, what they show, and what impact they have on the treatment of the patient.

Methods: The results of all nasopharyngeal cultures taken from children aged 0-12 years in the county of Skåne, Sweden, during 2018 were obtained. Medical charts from hospitals and primary care centres were used to determine why the cultures were taken and whether they resulted in a change of treatment.

Results: During 2018, 2200 nasopharyngeal cultures were taken, most of them during the winter season. Forty-one percent of children had on-going antibiotic treatment or had been treated with antibiotics in the previous two months. Acute otitis media (AOM) was the most common reason for taking a culture. The most frequently identified bacteria were Moraxella catarrhalis and Haemophilus influenzae. There was a positive correlation between M. catarrhalis on one hand and Streptococcus pneumoniae and H. influenzae on the other. Overall, bacterial resistance was rare. The presence of beta-lactamase negative ampicillin resistant H. influenzae was associated with recent or on-going antibiotics, whereas S. pneumoniae with decreased penicillin susceptibility were found less frequently in the same group of children. A positive culture resulted in a change of treatment in 29% of the cases.

Conclusion: Apart from playing a confirmatory role and monitoring the incidence of resistant bacteria, almost a third of the nasopharyngeal cultures analysed in this study contributed to decision-making. It therefore appears that bacterial sampling have a role in clinical practice. It would be valuable to study more closely why nasopharyngeal cultures are taken in during AOM and how the result affects the treatment.