International Journal of Pediatric Otorhinolaryngology
Colonization rate of bacteria in the throat of healthy infants
Introduction
The relationship between humans and their microbes is very complex. Resident micro-organisms are normally associated with a particular site and a particular animal host. Host factors (like defence mechanisms) and microbial features (virulence) will influence the result of the process of infection.
A microbe is a pathogen when infection results in disease. Colonization is also an infection but the relationship between the host and the micro-organism is commensal.
When relatively virulent organisms which are known as potential pathogens colonize a human host we consider the patient as a carrier and in many cases this situation is undesirable. Bacterial colonization of the upper respiratory tract occurs as early as the first months of life [1]. The human orophanynx is a primary ecological niche for various bacteria such as Streptococcus pneumoniae, Haemophilus spp., Staphylococcus aureus, coagulase negative staphylococci, β-haemolytic streptococci, Neisseria spp., α-haemolytic streptococci, Moraxella catherallis, Lactobacilli, Corynebacteria, anaerobes, Candida albicans and various protozoa [1]. These microorganisms may infect ordinarily sterile neighbouring sites and cause otitis media, conjunctivitis or sinusitis. Some of them may even penetrate the mucosa and cause invasive diseases such as pneumonia, sepsis or meningitis [1], [2], [3].
Children with recurrent episodes of otitis media have been shown to have a higher carrier rate of potentially pathogenic bacteria, including Streptococcus pneumoniae, non-typeable Haemophilus influenzae, Moraxella catarrhalis and Streptococcus group A, than healthy children [3], [4], [5].
It was possible to isolate, by throat culture, a type of capsulated Streptococcus pneumoniae, similar to that isolated from the middle ear, a short time before the onset of otitis media [6]. Furthermore, a correlation of 95–100% was found between the bacteria isolated from the middle ear and those obtained by a nasopharyngeal culture during an ear infection [6]. During outbreaks of meningitis in day-care centres caused by Haemophilus influenzae Type b, the pathogen was found in the throat of children who were in contact with the sick infants, but not in those who were not [7], [8]. During pneumococcal outbreaks in day care centres the pathogen was found in up to 86% of the healthy children in the centre [9]. In cases of tonsillitis caused by Streptococcus group A, the same pathogen was frequently found in the throat of healthy contacts [10].
The purpose of this study was to determine the current carrier state of healthy Israeli infants who are not exposed to infectious diseases in day care centres. The bacteria studied included the frequent pathogens in our area: β-haemolytic streptococci (groups A, C and G), Streptococcus pneumoniae, Haemophilus influenzae Type b, non-typeable Haemophilus influenzae, Neisseria meningitidis, and Staphylococcus aureus.
The frequency of the presence of these bacteria concurrently in the throat of healthy young children in Israel has not been reported earlier.
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Materials and methods
The study was approved by the ethics committee of Assaf Harofeh Medical Centre and the Israel Ministry of Health. Signed informed consent was obtained from the parents before enrolment.
Inclusion criteria included healthy children aged 1–24 months. The infants were examined for a routine follow-up in ten well-baby care clinics, where children are seen for vaccinations and periodic physical examination. These children were afebrile, and had no upper respiratory tract symptoms, tonsillar exudate,
Results
One thousand children aged 1–24 months (mean±S.D.=10±6 m) 530 males and 470 females were included in the study. Table 1 shows the frequency of the isolation of various pathogens from children's throats.
The 13 (1.3%) children with Streptococcus group A ranged in age from 3 to 21 months (mean±S.D.=10.4±7.5); six were in their first year of life, the youngest being a 3-month-old infant (mean±S.D.=5.5±3 months). Typing of Streptococcus group A for M precipitation and T agglutination was carried out
Discussion
In the present study we investigated the presence of several frequent pathogenic bacteria in the throat of healthy infants.
Pharingotonsillar flora is affected by many demographic factors like climate, age, the extent of exposure to infectious diseases, or vaccines.
A comparison of four sampling methods for detecting pharyngeal infection in symptomatic children showed that the nasopharyngeal swab seemed optimal for the detection of Streptococcus pneumoniae, for Haemophilus influenzae the
Acknowledgements
We would like to thank Zeev Gorodnitzky, MSc, and Zinaida Korenman, MSc, from the National Centre of Streptococci and Pneumococci Laboratories, Ministry of Health Central Laboratory, Jerusalem, Israel, for serotyping the isolates, and Shahnaz Zarini and Hani Moshe for typing the manuscript.
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