STREPTOCOCCUS PNEUMONIAE CARRIAGE RATE IN DENTAL PATIENTS 1249 STREPTOCOCCUS PNEUMONIAE CARRIAGE RATE IN HEALTHY PREADOLESCENT DENTAL PATIENTS

Introduction. Streptococcus pneumoniae is the major cause of death for pneumonia in the world, responsible 800,000 deaths annually among children and elderly. Most pneumonia caused by pneumococci are healthcare associated, while the remaining are community acquired. Airborne infections are frequent in dental healthcare settings, but data regarding the risk for pneumococci transmission are lacking. Aim. To estimate S. pneumoniae carriage rate among adolescent dental patients, in order to investigate the risk for pneumococci acquisition and spread in dental healthcare settings. Material and methods. 199 children aged 10-12 years attending the paediatric dentistry section of a dental hospital in Rome underwent oropharyngeal swab samples. Pneumococci were presumptively identified with cultural methods (growth on selective media, alpha haemolysis, bile solubility). Routine exposure to passive smoking, use of antibiotics, recent respiratory tract infections (RTIs) were anamnaestically investigated. Unadjusted and adjusted odds ratios (ORs) and individual probability to carry S. pneumoniae were assessed with logistic regression analysis. Results. Overall S. pneumoniae carriage rate was 11.6% (95% confidence interval, 95CI, 7.2-16.0%). RTIs were significantly associated with carriage (adjusted OR, 3.3; 95CI, 1.3-8.7), exposure to passive smoking (OR, 2.0; 95CI, 0.8-4.9), male gender (OR, 3.2; 95CI, 0.6-17.1) were marginally associated (0.05<p<0.20). According to the regression model, male patients with recent RTI history and routinely exposed to passive smoking yielded 58.2% probability to carry pneumococci. Conclusion. S. pneumoniae carriage rate in healthy preadolescent dental patients was moderately high. Patient’s profile could be helpful to identify potential carriers and to adopt transmission-based precautions.


Introduction
Streptococcus pneumoniae is a widespread colonizer of the upper respiratory tract, par ticularly in children younger than two years.Colonization of the human mucosa of the upper respiratory tract is determined by many factors, such as availability of resources (e.g., nutrients and space), defensive host factors, presence of toxins or harmful substances and type and num ber of established bacterial populations.For ex ample, Haemophilus influenzae and Staphylo coccus aureus, are other colonizers of the upper respiratory tract, which act in antagonism with S. pneumoniae colonization, while pre-existing pneumococci promote adhesion and coloniza tion of other pneumococci strains 1 .S. pneu moniae is transmitted from person to person by respiratory droplets.Environmental factors responsible for transmission are indoor crowd ing, associated viral infections, lower humidity and air pollution 2 .In the majority of children these microorganisms are not responsible for disease (see, for example 3-5).However, in sus ceptible individuals, S. pneumoniae is respon sible for mild infections, such as otitis media, sinusitis, conjunctivitis and even most serious diseases, such as pneumonia, meningitis, bac terial endocarditis 2 .The most famous example occurred during the deadly pandemic flu of 1918, when several millions of people from all over the world died by influenza-related pneu monia.The majority of these deaths are now attributed to pneumococcal super-infection 67 .Today, S. pneumoniae is the major cause of death for pneumonia in the world, allegedly re sponsible for 826,000 deaths annually among children younger than five years, particularly those with important co-morbidities, such as HIV infection or malnutrition, and, only in US, for 401,000 hospitalizations in elderly aged 65 years or older, particularly smokers, alcohol drinkers, subjects with diabetes, chronic lung disease and immunodeficiency [8][9] .
Pneumonia caused by pneumococci are as sociated with healthcare (HCAP, healthcareassociated pneumonia) or community acquired (CAP, community acquired pneumonia).HCAP definition is pneumonia developed in patients previously hospitalized in acute care hospitals for two or more days within ninety days of the infection, resided in a nursing home or long term care facility, received recent intravenous antibiotic therapy, chemotherapy, or wound care within the past thirty days of the current infection, or attended a hospital or haemodialy sis clinic 10 .S. pneumoniae is the most frequent etiological agent of HCAPs, being responsible for more than one fourth of all cases, while, for example, H. influenzae and S. aureus are re sponsible for one tenth and one fortieth, respec tively.Thus, S. pneumoniae shares the same ecological niche, the same pattern of transmis sion and similar risk factors, antibiotic resis tance, casefatality rate as methicillinresistant S. aureus (MRSA) 11 .
Since infections caused by pneumococci are airborne, it would not be surprising that their transmission occurs during dental therapy.For example, oral fluid retraction, which occurs in >70% cases when the dental turbine stops rotat ing, is responsible for aspiration of oral strepto cocci, non-pathogenic colonizers of the upper respiratory tract, in dental unit waterlines and subsequent spread in the environment during successive dental therapy 12 .The same pattern of transmission could be thought for pneumo cocci.However, the risk of infection in dental healthcare settings cannot be based on mere conjectures, but must be founded on the solid basis of scientific evidence 13 .Indeed, while data regarding MRSA in dental healthcare set tings are few, but sufficient to assess the risk for infection 14 , persistence in the environment 15 and effect of different control measures 16 , data regarding S. pneumoniae in dental healthcare settings are lacking and do not allow to assess whether these microorganism pose any risk for infection or whether preventive guidelines are necessary.In absence of direct evidence of as certained cases of infection transmission, indi rect evidence could be drawn by observational studies 14 .

Aim
The aim of this study was to investigate S. pneumoniae carriage rate among dental patients who could, therefore, be responsible for the contamination of the environment during dental therapy, thus promoting acquisition and spread of pneumococci at community level.

Material and Methods
A consecutive sample was selected from children aged 10-12 years attending the pae diatric dentistry section of a dental hospital in Rome (Italy).The minimum sample size was estimated assuming S. pneumoniae carriage rate of 8.5%, based on a previous survey among healthy Italian children aged six years 17 .With the highest acceptable margin of error of 5% and confidence interval of 95%, the sample size was set at 119 subjects.The study protocol was approved by the ethic committee of the dental hospital and written informed consent to nasal swabbing and anamnestic data collection was obtained from children's parents or guardians.
The morning of the appointment and before the dental treatment, participating children un derwent an oropharyngeal sample which was collected by one of the authors expert in micro biological procedures and trained for this pur pose.The swab was inserted through the mouth and placed on the posterior wall of pharynx and on tonsils for at least five seconds, paying at tention not to touch uvula and tongue.Children must not assume antibiotics or other antimicro bials during one week before the sampling oc casion and must not drink or eat anything after breakfast.A questionnaire was administered to the parent or guardian by one of the authors and was used to obtain demographic and clini cal characteristics of the enrolled children.The questions were 1) development of respiratory tract infections (RTI-rhinitis, tonsillitis, laryn gitis, acute otitis media, sinusitis, acute bron chitis, pneumonia) during the month before the sampling occasion; 2) assumption of antibiot ics or other antimicrobial the month before the sampling occasion; 3) daily exposure to passive smoking at home.
The swabs were immediately plated on plates containing Columbia Agar supplemented with 5% sheep blood (Becton Dickinson Ita lia, Buccinasco, Italy), 5 μg/mL gentamicin and were incubated in 10% CO2 atmosphere at 37°C for 24 h.Alpha-haemolytic colonies were gram stained and tested for bile solubility add ing few drops of 2% sodium desoxycholate so lution (Becton Dickinson Italia) on some typi cal colonies.Plates were then incubated at 37°C for 30 min.Disappearance of colonies leaving areas of alpha-haemolysis was indicative of positive test 18 .Further identification tests were not made, therefore, positive samples were considered presumptively positive.This option decreased the internal validity of this study, as uncertainty could lead to S. pneumoniae car riage rate estimate artificially higher or lower than the true rate.For this reason, in order to increase the internal validity of the study leav ing unchanged the external validity, that is, the chance to extend the present prevalence es timate to Italian healthy children aged 10-12 years, the power of the test was increased by increasing the sample size from 119 to 186 sub jects, which resulted in a decrease in the margin of error from 5% to 4% 19 .
Presumptive S. pneumoniae carriage rate was estimated with 95% confidence interval (95CI).The association of S. pneumoniae car riage with age class, gender, RTI, routine ex posure to passive smoking and recent antibiotic therapy was initially assessed with logistic re gression analysis, which provided the odds ra tios (ORs) unadjusted for covariates.Multiple logistic regression analysis was then used to as sess the adjusted ORs.Collinearity between ex planatory variables was investigated using the Spearman's correlation coefficient ρ.If values higher than 0.5 were detected, only one of the two variables was used in the regression model.Robustness of results was investigated through pseudo-R2 and likelihood ratio χ2 test.
Since the aim of this study was to decrease the chance that airborne pneumococci are spread in the environment of the dental health care settings during therapy, thus decreasing the diffusion of these microorganisms at commu nity level, using the coefficients estimated by the multiple regression analysis a probabilistic model was built which provided the chance (ex pressed in percentage) that a child was S. pneu moniae carrier according to the aforementioned anamnestic variables.Only variables which provided p-values lower than 0.2 in the mul tiple logistic regression model were considered.

Results
The study was made between September and December 2011.The number of invited children was 223.Parents or guardians of 24 of them did not provide the consent to swab bing (n=15), anamnestic data collection (n=4), or both (n= 5).One hundred ninety-nine chil dren remained and were included in the sample (participation rate, 89.2%), their mean age was 11.3 years, almost one half of them was aged 12 years.Females were 106 and males 93 (Table 1).Incidence of reported RTIs during the month before the sampling occasion was 27%, while 8.5% assumed antibiotics in the same period.Routine exposure to passive smoking was high, namely, 35%.
S. pneumoniae carriage rate was 11.6% (Ta ble 2), with minimal differences between the three age classes, while carriage rate was higher in males than in females (12.9% vs. 10.4%).The unadjusted ORs for presumptive pneu mococci carriage were non-significant exclud ing for subjects with recent RTIs (OR, 2.8; 95CI, 1.2-6.9)(Table 3).Exposure to routine passive smoking resulted in a marginally significant association with carriage (unadjusted OR, 1.82; 95CI, 0.8-4.4;p=0.18).Adjustment for covariates provided an increase in the OR estimates for the most important variables, that is, recent RTIs (OR, 3.3; 95CI, 1.3-8.7),routine exposure to passive smoking (OR, 2.0; 95CI, 0.8-4.9)and male gender (OR, 3.2; 95CI, 0.6-17.1).These three variables were associated with pneumococci carriage with p<0.20 and were used in the probability model.Probability of carrying S. pneumoniae was the highest for males routinely exposed to passive smoking and with recent RTIs (58%) (Table 4) and was also high among males with recent RTIs (41%) and females routinely ex posed to passive smoking and with recent RTIs (30%).Conversely, in females with no episodes of RTIs and not exposed to passive smoking the chance to carry pneumococci was minimal (6%).

Discussion
The present study is one of the papers pre sented at the workshop "Advances in Infection Epidemiology and Control in Dental Healthcare Settings", Department of Public Health and In fectious Diseases, Sapienza University, Rome, Italy on February 9th, 2013 2026 .
The estimated S. pneumoniae carriage rate in healthy preadolescents was between 7% and 16%, suggesting that these microorganisms are likely to be spread in dental healthcare set tings.Carriage rate studies in young individu als are not frequent.Oropharyngeal carriage rate among 179 medical students from Turkey As previously noted, studies on the risk for S. pneumoniae infection among dental patients and staff are lacking.Therefore, it is not possi ble to make any convincing speculation regard ing the necessity of specific control measures.The present data allowed to design the profile of potential S. pneumoniae carriers among young dental patients.Indeed, male subjects with re cent RTI and daily exposure to passive smoking are more likely to be S. pneumoniae carriers.These predisposing characteristics are cor roborated by a previous Italian study made on young children 17 .In special dental healthcare settings where immune-compromised patients are generally treated, such as elderly, hospital ized patients, HIV positive subjects, oncologic patients, it is advisable to apply the so called transmission-based precautions 32 .Pneumococ cal vaccination is one of these precautions, al though polysaccharide pneumococcal vaccines do not seem totally effective in preventing in vasive pneumococcal disease and death 33 and the Infectious Disease Society of America does not recommend vaccination in any category of healthcare workers, therefore including dental healthcare workers, but recommends vacci nation for adults older than 65 years 34 .Influ enza vaccination, useful in preventing HCAP and CAP, including those cases attributable to S. pneumoniae, is probably more adequate in preventing pneumococcal transmission and in fection, because it decreases the probability to develop RTIs.

Conclusion
The present study demonstrated that S. pneumoniae carriage rate in healthy preadoles cent dental patients was moderately high and that such rate is higher in subjects with history of recent RTIs.Patient's profile could be help ful to identify potential carriers and to adopt transmission-based precautions, although the risk for infection for dental patients and staff is unknown.It is prudent that control of airborne microorganisms and pneumococcal and influ enza vaccinations are made by dental health care workers who practice in special care units.

Table 1 .
General characteristics of the 199 sampled children.

Table 3 .
Unadjusted and adjusted odds ratios (ORs) of the effects of age, gender, incidence of RTIs during the last month, use of antibiotics during the last month and routine exposure to passive smoking on carriage of presumptive S. pneumoniae.

Table 4 .
Probability of carrying S. pneumoniae according to gender, incidence of RTIs during the last month and routine exposure to passive smoking.Categories were ordered according to decreasing probability.