Modeling Community- and Individual-Level Effects of Child-Care Center Attendance on Pneumococcal Carriage

Investigation of Concurrent Pneumococcal Meningitis in Two Children Attending the Same Day-Care Center

Only a few clusters of invasive pneumococcal disease have been described globally in children, and most of these cases occurred before pneumococcal vaccination implementation. Two unusual cases of pneumococcal meningitis, occurring in the same daycare center over a 3-day period, were reported. Both cerebrospinal fluid (CSF) were sent to the National reference center for pneumococci. In addition, we decided to perform a pneumococcal carriage study on all children and staff of the daycare center to analyze the pneumococcal serotypes circulating in this DCC and to discuss an antibiotic chemoprophylaxis. CSF culture was positive for pneumococcus, and serotype 25A was identified by latex agglutination. The second case had negative CSF culture, but CSF antigen test and gene amplification results were positive for Streptococcus pneumoniae. Serotype 12F was identified by using molecular biology. The absence of correlation between these strains was confirmed by multi-locus sequence typing. In the carriage study, we included 29 children (median age 1.9 years, interquartile range 1.4-2.5) and 10 adults. Among the children, 24 carried Streptococcus pneumoniae (83%). The main serotypes isolated were 23A for 6 children and 25A for 5 children; serotypes were non-typeable for 3 children. Only 1 of 10 adults tested carried Streptococcus pneumoniae (serotype 12F). Despite this temporo-spatial pattern, the cases were unrelated and not due to carriage of a particular serotype. No specific action has been taken for the other children attending this DCC, and no other case of bacterial meningitis occurred.

Impact of private use of the 13-valent pneumococcal conjugate vaccine (PCV13) on pneumococcal carriage among Portuguese children living in urban and rural regions

In Portugal, the 13-valent pneumococcal conjugate vaccine (PCV13) was commercially available between 2010 and 2015, following a decade of private use of PCV7. We evaluated changes on serotype distribution and antimicrobial susceptibility of pneumococci carried by children living in two regions of Portugal (one urban and one rural). Three epidemiological periods were defined: pre-PCV13 (2009-2010), early-PCV13 (2011-2012), and late-PCV13 (2015-2016). Nasopharyngeal samples (n = 4,232) were obtained from children 0-6 years old attending day-care centers. Private use of PCVs was very high in both regions (>75%). Pneumococcal carriage remained stable and high over time (62.1%, 62.4% and 61.6% (p = 0.909) in the urban region; and 59.8%, 62.8%, 59.5% (p = 0.543) in the rural region). Carriage of PCV7 serotypes remained low (5.3%, 7.8% and 4.3% in the urban region; and 2.5%, 3.7% and 4.8% in the rural region). Carriage of PCV13 serotypes not targeted by PCV7 decreased in both the urban (16.4%, 7.3%, and 1.6%; p < 0.001) and rural regions (13.2%, 7.8%, and 1.9%; p < 0.001). This decline was mostly attributable to serotype 19A (14.1%, 4.4% and 1.3% in the urban region; and 11.1%, 3.6% and 0.8% in the rural region, both p < 0.001). Serotype 3 declined over time in the urban region (10.1%, 4.4%, 0.8%; p < 0.001) and had no obvious trend in the rural region (4.2%, 6.7%, 2.4%; p = 0.505). Serotype 6C decreased in both regions while serotypes 11D, 15A/B/C, 16F, 21, 22F, 23A/B, 24F, 35F, and NT were the most prevalent in the late-PCV13 period. Intermediate resistance to penicillin and non-susceptibility to erythromycin decreased significantly in both regions (19.5%, 13.3%, and 9.3%; and 25.4%, 25.9%, and 13.4%; both p < 0.001, respectively in the urban region; and 12.4%, 11.1%, and 2.8% (p < 0.001); and 15.3%, 14.7%, and 9.2% (p = 0.037), respectively, in the rural region). In conclusion, private use of PCV13 led to significant changes on the pneumococcal population carried by children in Portugal.

Serotypes and Vaccine Coverage of Streptococcus Pneumoniae Colonization in the Nasopharynx of Thai Children in Congested Areas in Chiang Mai

Streptococcus pneumoniae causes around 10% of all deaths in children younger than five years of age. This study aimed to examine the serogroups/serotypes of S. pneumoniae colonization and vaccine serotype coverage of this organism among Thai children. Nasopharyngeal swabs of children less than or equal to 15 years of age were obtained in congested areas in Chiang Mai from 1 February 2013 to 1 August 2013. The serotyping of S. pneumoniae isolates was performed using the ImmuLex™ kit and the vaccine serotype coverage for this organism was evaluated. A total of 292 children were enrolled. One hundred and thirty children (44.5%) had nasopharyngeal colonization with Streptococcus pneumoniae. Eighty-seven (66.9%) isolates were from children younger than five years of age, seventeen (13.1%) were from children aged 6-10 years, and twenty-six (20%) were from children aged 11-15 years. The five most common serogroups/serotypes isolated were 6 (6A, 6B, 6C) (46.1%), 23 (23F, 23A, 23B) (14.6%), 19 (19F, 19A, 19B, 19C) (8.5%), 15 (15F, 15A, 15B, 15C) (6.9%), and 14 (6.1%). Vaccine serotype coverages in pneumococcal conjugate vaccines (PCV):PCV7, PCV10, and PCV13 were 79.1%, 83.6%, and 85.9%, respectively. There were significant increases in coverage between PCV7 and PCV10 (from 79.1% to 83.6%, p < 0.001), PCV7 and PCV13 (from 79.1% to 85.9%, p < 0.001), and PCV10 and PCV13 (from 83.6% to 85.9%, p < 0.001). The majority of pneumococcal serogroup/serotype colonization in the nasopharynx of Thai children in the studied areas was included in the current licensed pneumococcal conjugated vaccines (PCVs). PCV vaccination should be considered for high-risk children to reduce the incidence of invasive pneumococcal disease among Thai children.

Estimating the contribution of different age strata to vaccine serotype pneumococcal transmission in the pre vaccine era: a modelling study

BACKGROUND

Herd protection through interruption of transmission has contributed greatly to the impact of pneumococcal conjugate vaccines (PCVs) and may enable the use of cost-saving reduced dose schedules. To aid PCV age targeting to achieve herd protection, we estimated which population age groups contribute most to vaccine serotype (VT) pneumococcal transmission.

METHODS

We used transmission dynamic models to mirror pre-PCV epidemiology in England and Wales, Finland, Kilifi in Kenya and Nha Trang in Vietnam where data on carriage prevalence in infants, pre-school and school-aged children and adults as well as social contact patterns was available. We used Markov Chain Monte Carlo methods to fit the models and then extracted the per capita and population-based contribution of different age groups to VT transmission.

RESULTS

We estimated that in all settings, < 1-year-old infants cause very frequent secondary vaccine type pneumococcal infections per capita. However, 1-5-year-old children have the much higher contribution to the force of infection at 51% (28, 73), 40% (27, 59), 37% (28, 48) and 67% (41, 86) of the total infection pressure in E&W, Finland, Kilifi and Nha Trang, respectively. Unlike the other settings, school-aged children in Kilifi were the dominant source for VT infections with 42% (29, 54) of all infections caused. Similarly, we estimated that the main source of VT infections in infants are pre-school children and that in Kilifi 39% (28, 51) of VT infant infections stem from school-aged children whereas this was below 15% in the other settings.

CONCLUSION

Vaccine protection of pre-school children is key for PCV herd immunity. However, in high transmission settings, school-aged children may substantially contribute to transmission and likely have waned much of their PCV protection under currently recommended schedules.

Determinants of high residual post-PCV13 pneumococcal vaccine-type carriage in Blantyre, Malawi: a modelling study

BACKGROUND

In November 2011, Malawi introduced the 13-valent pneumococcal conjugate vaccine (PCV13) into the routine infant schedule. Four to 7 years after introduction (2015-2018), rolling prospective nasopharyngeal carriage surveys were performed in the city of Blantyre. Carriage of Streptococcus pneumoniae vaccine serotypes (VT) remained higher than reported in high-income countries, and impact was asymmetric across age groups.

METHODS

A dynamic transmission model was fit to survey data using a Bayesian Markov-chain Monte Carlo approach, to obtain insights into the determinants of post-PCV13 age-specific VT carriage.

RESULTS

Accumulation of naturally acquired immunity with age and age-specific transmission potential were both key to reproducing the observed data. VT carriage reduction peaked sequentially over time, earlier in younger and later in older age groups. Estimated vaccine efficacy (protection against carriage) was 66.87% (95% CI 50.49-82.26%), similar to previous estimates. Ten-year projected vaccine impact (VT carriage reduction) among 0-9 years old was lower than observed in other settings, at 76.23% (CI 95% 68.02-81.96%), with sensitivity analyses demonstrating this to be mainly driven by a high local force of infection.

CONCLUSIONS

There are both vaccine-related and host-related determinants of post-PCV13 pneumococcal VT transmission in Blantyre with vaccine impact determined by an age-specific, local force of infection. These findings are likely to be generalisable to other Sub-Saharan African countries in which PCV impact on carriage (and therefore herd protection) has been lower than desired, and have implications for the interpretation of post-PCV carriage studies and future vaccination programs.

Resistance diagnostics as a public health tool to combat antibiotic resistance: A model-based evaluation

Rapid point-of-care resistance diagnostics (POC-RD) are a key tool in the fight against antibiotic resistance. By tailoring drug choice to infection genotype, doctors can improve treatment efficacy while limiting costs of inappropriate antibiotic prescription. Here, we combine epidemiological theory and data to assess the potential of resistance diagnostics (RD) innovations in a public health context, as a means to limit or even reverse selection for antibiotic resistance. POC-RD can be used to impose a nonbiological fitness cost on resistant strains by enabling diagnostic-informed treatment and targeted interventions that reduce resistant strains' opportunities for transmission. We assess this diagnostic-imposed fitness cost in the context of a spectrum of bacterial population biologies and find that POC-RD have a greater potential against obligate pathogens than opportunistic pathogens already subject to selection under "bystander" antibiotic exposure during asymptomatic carriage (e.g., the pneumococcus). We close by generalizing the notion of RD-informed strategies to incorporate carriage surveillance information and illustrate that coupling transmission-control interventions to the discovery of resistant strains in carriage can potentially select against resistance in a broad range of opportunistic pathogens.

Associations of Neighborhood-Level Social Determinants of Health with Bacterial Infections in Young, Febrile Infants

OBJECTIVE

To examine the sociodemographic characteristics of one population of young, febrile infants and identify associations between neighborhood-level social determinants of health (SDHs) with bacterial infections.

STUDY DESIGN

This was a retrospective cross sectional study of all infants ≤90 days old with a temperature of ≥38°C who presented in 2014 to the emergency department of an urban children's hospital in a large east coast city. The primary outcome was the presence of a bacterial infection, defined as a positive urine, blood, or cerebrospinal fluid culture that was treated clinically as a pathogen. The home address of each infant was geocoded and linked to neighborhood data based on census tract. Neighborhood-level SDHs included deprivation index, median household income, poverty, childhood poverty, social capital, and crowded housing. Associations were estimated using generalized estimating equations and negative binomial regression analysis. Models were adjusted for age, prematurity, and race/ethnicity.

RESULTS

Of 232 febrile infants, the median age was 54 days, 58% were male, 49% were Hispanic, and 88% had public health insurance; 31 infants (13.4%) had a bacterial infection. In the adjusted analyses, the risk of bacterial infection among infants from neighborhoods with high rates of childhood poverty was >3 times higher (relative risk, 3.16; 95% CI, 1.04-9.6) compared with infants from neighborhoods with low rates of childhood poverty.

CONCLUSIONS

Our findings suggest that SDHs may be associated with bacterial infections in young, febrile infants. If confirmed in subsequent studies, the inclusion of SDHs in predictive tools may improve accuracy in detecting bacterial infections among young, febrile infants.

Risk factors for carriage of Streptococcus pneumoniae in children

Background

During the past decades Streptococcus pneumoniae has developed significant resistance to many classes of antimicrobial drugs. Potential risk factors for colonization of the nasopharynx by Streptococcus pneumoniae in children and for carriage of drug resistant strains were examined.

Methods

Between 2007 and 2008 nasopharyngeal swabs were collected from 402 children 6 months to 5 years old visiting the public sector immunization centers and outpatient departments as well as offices of paediatricians from private practice in Nicosia district in Cyprus. Information on demographic characteristics and potential risk factors of participating children were collected using a standardized questionnaire distributed to parents.

Results

In multivariable analyses we found that attendance at day care center, having siblings in the family and having both parents originating from Cyprus, statistically increased the risk of pneumococcal colonization. Full immunization with PCV7 appears to be a protective factor against colonization by pneumococcus. Previous administration of antimicrobials during the last month prior to specimen collection appeared to be the most consistent risk factor for carrying a non susceptible strain of Streptococcus pneumoniae to either penicillin or erythromycin. Factors such as age, nationality, previous or current breastfeeding, passive exposure to cigarette smoke and attendance in a day care center do not appear as independent risk factors for colonization by non susceptible strains.

Conclusions

Prudent use of antibiotics especially for upper respiratory tract infections in children as well as increased vaccination coverage by the pneumococcal conjugate vaccines could prove effective in reducing levels of colonization by drug resistant pneumococcal strains.

Geographic variation in pneumococcal vaccine efficacy estimated from dynamic modeling of epidemiological data post-PCV7

Although mean efficacy of multivalent pneumococcus vaccines has been intensively studied, variance in vaccine efficacy (VE) has been overlooked. Different net individual protection across settings can be driven by environmental conditions, local serotype and clonal composition, as well as by socio-demographic and genetic host factors. Understanding efficacy variation has implications for population-level effectiveness and other eco-evolutionary feedbacks. Here I show that realized VE can vary across epidemiological settings, by applying a multi-site-one-model approach to data post-vaccination. I analyse serotype prevalence dynamics following PCV7, in asymptomatic carriage in children attending day care in Portugal, Norway, France, Greece, Hungary and Hong-Kong. Model fitting to each dataset provides site-specific estimates for vaccine efficacy against acquisition, and pneumococcal transmission parameters. According to this model, variable serotype replacement across sites can be explained through variable PCV7 efficacy, ranging from 40% in Norway to 10% in Hong-Kong. While the details of how this effect is achieved remain to be determined, here I report three factors negatively associated with the VE readout, including initial prevalence of serotype 19F, daily mean temperature, and the Gini index. The study warrants more attention on local modulators of vaccine performance and calls for predictive frameworks within and across populations.

Periodic cycles of pneumococcal serotypes carried by children before and after 7-valent pneumococcal conjugate vaccine

BACKGROUND

Periodic cycles in the serotype-specific incidence of invasive pneumococcal disease have been described but less is known in carriage.

METHODS

We analyzed serotype carriage prevalence among children 0-6 years old over a 15-year period that included pre-PCV7 data and a decade of PCV7 use. Mixed generalized additive models were used to study periodic cycles and how PCV7 impacted on them.

RESULTS

Pneumococcal carriage data of 7,463 children were analyzed. Periodic cycles ranging from 3 to 6 years were observed for PCV7-serotypes (VT) 14, 19F and 23F and for non-PCV7 types (NVT) 3, 6A, 6C, 11A, and NT. An indirect impact of PCV7 on periodic cycles of NVT was observed and could be translated in three ways: (i) a higher amplitude in the PCV7 period (serotypes 3 and 11A), (ii) sustained increase in the prevalence of carriage (serotypes 6C, 19A and NT) and (iii) an increase in the inter-epidemic period (serotypes 3, 6A and NT). An increase in the child's mean age of carriage of VTs 6B, 19F and 23F was observed. Serotypes 3, 6C, 11A and 15A became more frequent in ages previously associated with carriage of VTs.

CONCLUSIONS

Periodic cycles among serotypes frequently carried exist and can be modeled. These cycles can be perturbed upon introduction of PCVs and can lead to shifts in the mean age of carriage. Cyclic re-emergence of VTs can occur in settings with non-universal vaccine use. These results should be taken into account when interpreting surveillance data on pneumococcal carriage.

Increased incidence of adult pneumococcal pneumonia during school holiday periods

Child contact is a recognised risk factor for adult pneumococcal disease. Peaks in invasive pneumococcal disease incidence observed during winter holidays may be related to changes in social dynamics. This analysis was conducted to examine adult pneumococcal community-acquired pneumonia (CAP) incidence during school holiday periods.

Between September 2008 and 2013, consecutive adults admitted to hospitals covering the Greater Nottingham area with a diagnosis of CAP were studied. Pneumococcal pneumonia was detected using culture and antigen detection methods.

Of 2221 adults studied, 575 (25.9%) were admitted during school holidays and 643 (29.0%) had pneumococcal CAP. CAP of pneumococcal aetiology was significantly more likely in adults admitted during school holidays compared to term time (35.3% versus 26.7%; adjusted OR 1.38, 95% CI 1.11–1.72, p=0.004). Over the 5-year period, the age-adjusted incidence of hospitalised pneumococcal CAP was higher during school holidays compared to term time (incident rate ratio 1.35, 95% CI 1.14–1.60, p<0.001); there was no difference in rates of all-cause CAP or non-pneumococcal CAP. Reported child contact was higher in individuals with pneumococcal CAP admitted during school holidays compared to term time (42.0% versus 33.7%, OR 1.43, 95% CI 1.00–2.03, p=0.046).

Further study of transmission dynamics in relation to these findings and to identify appropriate intervention strategies is warranted.

School holiday periods are associated with an increased incidence of adult pneumococcal community-acquired pneumoniahttp://ow.ly/JiAb3089Gii

Long-term effects of penicillin resistance and fitness cost on pneumococcal transmission dynamics in a developed setting

BACKGROUND

The increasing prevalence of penicillin non-susceptible pneumococci (PNSP) throughout the world threatens successful treatment of infections caused by this important bacterial pathogen. The rate at which PNSP clones spread in the community is thought to mainly be determined by two key determinants; the volume of penicillin use and the magnitude of the fitness cost in the absence of treatment. The aim of the study was to determine the impacts of penicillin consumption and fitness cost on pneumococcal transmission dynamics in a developed country setting.

METHODS

An individual-based network model based on real-life demographic data was constructed and applied in a developed country setting (Sweden). A population structure with transmission of carriage taking place within relevant mixing groups, i.e. families, day care groups, school classes, and other close contacts, was considered to properly assess the transmission dynamics for susceptible and PNSP clones. Several scenarios were simulated and model outcomes were statistically analysed.

RESULTS

Model simulations predicted that with an outpatient penicillin use corresponding to the sales in Sweden 2010 (118 recipes per 1,000 inhabitants per year), the magnitude of a fitness cost for resistance must be at least 5% to offset the advantage of penicillin resistance. Moreover, even if there is a fitness cost associated with penicillin resistance, a considerable reduction of penicillin usage appears to be required to significantly decrease the incidence of PNSP in a community.

CONCLUSION

The frequency of PNSP clones is hard to reverse by simply reducing the penicillin consumption even if there is a biological cost associated with resistance. However, because penicillin usage does promote further spread of PNSP clones, it is important to keep down penicillin consumption considering future resistance problems.

Seasonal Dynamics of the Airborne Bacterial Community and Selected Viruses in a Children's Daycare Center

Children’s daycare centers appear to be hubs of respiratory infectious disease transmission, yet there is only limited information about the airborne microbial communities that are present in daycare centers. We have investigated the microbial community of the air in a daycare center, including seasonal dynamics in the bacterial community and the presence of specific viral pathogens. We collected filters from the heating, ventilation, and air conditioning (HVAC) system of a daycare center every two weeks over the course of a year. Amplifying and sequencing the 16S rRNA gene revealed that the air was dominated by Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes that are commonly associated with the human skin flora. Clear seasonal differences in the microbial community were not evident; however, the community structure differed when the daycare center was closed and unoccupied for a 13-day period. These results suggest that human occupancy, rather than the environment, is the major driver in shaping the microbial community structure in the air of the daycare center. Using PCR for targeted viruses, we detected a seasonal pattern in the presence of respiratory syncytial virus that included the period of typical occurrence of the disease related to the virus; however, we did not detect the presence of adenovirus or rotavirus at any time.

Population Dynamics of Patients with Bacterial Resistance in Hospital Environment

During the past decades, the increase of antibiotic resistance has become a major concern worldwide. The researchers found that superbugs with new type of resistance genes (NDM-1) have two aspects of transmission characteristics; the first is that the antibiotic resistance genes can horizontally transfer among bacteria, and the other is that the superbugs can spread between humans through direct contact. Based on these two transmission mechanisms, we study the dynamics of population in hospital environment where superbugs exist. In this paper, we build three mathematic models to illustrate the dynamics of patients with bacterial resistance in hospital environment. The models are analyzed using stability theory of differential equations. Positive equilibrium points of the system are investigated and their stability analysis is carried out. Moreover, the numerical simulation of the proposed model is also performed which supports the theoretical findings.

Improving the modeling of disease data from the government surveillance system: a case study on malaria in the Brazilian Amazon

The study of the effect of large-scale drivers (e.g., climate) of human diseases typically relies on aggregate disease data collected by the government surveillance network. The usual approach to analyze these data, however, often ignores a) changes in the total number of individuals examined, b) the bias towards symptomatic individuals in routine government surveillance, and; c) the influence that observations can have on disease dynamics. Here, we highlight the consequences of ignoring the problems listed above and develop a novel modeling framework to circumvent them, which is illustrated using simulations and real malaria data. Our simulations reveal that trends in the number of disease cases do not necessarily imply similar trends in infection prevalence or incidence, due to the strong influence of concurrent changes in sampling effort. We also show that ignoring decreases in the pool of infected individuals due to the treatment of part of these individuals can hamper reliable inference on infection incidence. We propose a model that avoids these problems, being a compromise between phenomenological statistical models and mechanistic disease dynamics models; in particular, a cross-validation exercise reveals that it has better out-of-sample predictive performance than both of these alternative models. Our case study in the Brazilian Amazon reveals that infection prevalence was high in 2004–2008 (prevalence of 4% with 95% CI of 3–5%), with outbreaks (prevalence up to 18%) occurring during the dry season of the year. After this period, infection prevalence decreased substantially (0.9% with 95% CI of 0.8–1.1%), which is due to a large reduction in infection incidence (i.e., incidence in 2008–2010 was approximately one fifth of the incidence in 2004–2008).We believe that our approach to modeling government surveillance disease data will be useful to advance current understanding of large-scale drivers of several diseases.

Disease data collected by the government surveillance system are frequently used to understand the influence of large-scale phenomena (e.g., climate) on human health because these data often have a large temporal and/or geographical span. The down side is that a) these data are often biased towards individuals that come to the health facilities (i.e., symptomatic individuals); and b) the number of individuals examined can vary substantially regardless of concurrent changes in prevalence or incidence (e.g., due to shortage of personnel or supplies in health facilities), directly impacting the number of disease cases detected. Current modeling approaches typically ignore these peculiarities of the government data. Furthermore, current approaches do not take into account that observations directly influence disease dynamics since individuals with a positive diagnosis are often subsequently treated for the disease. In this article, we develop a novel model to circumvent these shortcomings and apply it to simulated data, highlighting how inference on infection incidence and prevalence might be misleading when some of the issues mentioned above are ignored. Finally, we illustrate this model using malaria data from the Brazilian Amazon, revealing the strong role of precipitation on infection prevalence seasonality and striking patterns in infection incidence.

Do community-level predictors of pneumococcal carriage continue to play a role in the conjugate vaccine era?

This paper examined whether previously identified community-level factors (high proportion of crowded households and/or persons below the poverty level) remained associated with childhood pneumococcal carriage in the heptavalent pneumococcal conjugate vaccine (PCV7) era. Using logistic regression, individual factors were used to develop base models to which community-level factors were added to evaluate impact on pneumococcal carriage within two paediatric study cohorts from Massachusetts (urban Boston, outside Boston). Six years after introduction of universal childhood PCV7 vaccination, we found no consistent evidence that census tract characteristics (e.g. population size and density, age and race distribution, percent participating in group childcare, parental education, percent lacking in-unit plumbing, poverty, and community stability) affected odds of pneumococcal carriage when added to individual predictors (e.g. younger age, current respiratory tract infections, and attendance in group childcare). How community-level factors influence pneumococcal carriage continues to change in the era of increasing immunization coverage.

Risk of invasive pneumococcal disease varies by neighbourhood characteristics: implications for prevention policies

This study investigates neighbourhood variation in rates of pneumococcal bacteraemia and community-level factors associated with neighbourhood heterogeneity in disease risk. We analysed data from 1416 adult and paediatric cases of pneumococcal bacteraemia collected during 2005-2008 from a population-based hospital surveillance network in metropolitan Philadelphia. Cases were geocoded using residential address to measure disease incidence by neighbourhood and identify potential neighbourhood-level risk factors. Overall incidence of pneumococcal bacteraemia was 36∙8 cases/100,000 population and varied significantly (0-67∙8 cases/100,000 population) in 281 neighbourhoods. Increased disease incidence was associated with higher population density [incidence rate ratio (IRR) 1∙10/10,000 people per mile², 95% confidence interval (CI) 1∙0-1∙19], higher percent black population (per 10% increase) (IRR 1∙07, 95% CI 1∙04-1∙09), population aged ≤5 years (IRR 3∙49, CI 1∙8-5∙18) and population aged ≥65 years (IRR 1∙19, CI 1∙00-1∙38). After adjusting for these characteristics, there was no significant difference in neighbourhood disease rates. This study demonstrates substantial small-area variation in pneumococcal bacteraemia risk that appears to be explained by neighbourhood sociodemographic characteristics. Identifying neighbourhoods with increased disease risk may provide valuable information to optimize implementation of prevention strategies.

[Epidemiology of nasopharyngeal carriage of Streptococcus pneumoniae in children < 6 years old in Seville]

INTRODUCTION

The aim of this investigation was to study the epidemiology of nasopharyngeal (NP) colonization with Streptococcus pneumoniae after the introduction of the heptavalent pneumococcal conjugate vaccine (PCV7).

METHODS

NP swabs were obtained from 848 children aged 6 months to six years seen in four primary care centres (healthy children) and in two emergency depeartments (sick children) from Seville. The study was conducted between February 2005 and June 2008.

RESULTS

A total of 278 (33%) children carried S. pneumoniae. Pneumococcal colonization was independently predicted by school attendance or child care participation (OR 2.21; 95% CI 1.54- 3.15; P=.0001) and younger age. Recent antibiotic use was protective (OR 0.68; 95% CI 0.48-0.94; P=.02). PCV7 uptake was 41%. Risk of carriage of PCV7- type pneumococci was lower among children who had received ≥1 dose of PCV7 (7% vs 29%; [OR 0.21; 95% CI 0.09-0.49; P=.0001]). The proportion of pneumococcal isolates with oral penicillin non-susceptibility and amoxicillin resistance were 33% and 3%, respectively. Amoxicillin resistance in colonized children was associated with prior antibiotic usage (OR 4.29; 95% CI 1.09-20.02).

CONCLUSIONS

NP colonization rates with PCV7- type pneumococci were low compared to those found in studies prior to PCV7 introduction, both in vaccinated and unvaccinated subjects. Factors related to age and overcrowding increased the prevalence of pneumococcal carriage. Use of antibiotics reduced the overall carriage of pneumococci, but was a risk factor for colonization with amoxicillin resistant pneumococci.

Contribution of mathematical modeling to the fight against bacterial antibiotic resistance

PURPOSE OF REVIEW

Modeling of antibiotic resistance in pathogenic bacteria responsible for human disease has developed considerably over the last decade. Herein, we summarize the main published studies to illustrate the contribution of models for understanding both within-host and population-based phenomena. We then suggest possible topics for future studies.

RECENT FINDINGS

Model building of bacterial resistance has involved epidemiologists, biologists and modelers with two different objectives. First, modeling has helped largely in identifying and understanding the factors and biological phenomena responsible for the emergence and spread of resistant strains. Second, these models have become important decision support tools for medicine and public health.

SUMMARY

Major improvements of models in the coming years should take into account specific pathogen characteristics (resistance mechanisms, multiple colonization phenomena, cooperation and competition among species) and better description of the contacts associated with transmission risk within populations.

New approaches to estimating national rates of invasive pneumococcal disease

National infectious disease incidence rates are often estimated by standardizing locally derived rates using national-level age and race distributions. Data on other factors potentially associated with incidence are often not available in the form of patient-level covariates. Including characteristics of patients' area of residence may improve the accuracy of national estimates. The authors used data from the Centers for Disease Control and Prevention's Active Bacterial Core Surveillance program (2004-2005), adjusted for census-based variables, to estimate the national incidence of invasive pneumococcal disease (IPD). The authors tested Poisson and negative binomial models in a cross-validation procedure to select variables best predicting the incidence of IPD in each county. Including census-level information on race and educational attainment improved the fit of both Poisson and negative binomial models beyond that achieved by adjusting for other census variables or by adjusting for an individual's race and age alone. The Poisson model with census-based predictors led to a national estimate of IPD of 16.0 cases per 100,000 persons as compared with 13.5 per 100,000 persons using an individual's age and race alone. Accuracy of, and confidence intervals for, these estimates can only be determined by obtaining data from other randomly selected US counties. However, incorporating census-derived characteristics should be considered when estimating national incidence of IPD and other diseases.

A mathematical model for the spread of Strepotococcus pneumoniae with transmission dependent on serotype

We examine a mathematical model for the transmission of Streptococcus Pneumoniae amongst young children when the carriage transmission coefficient depends on the serotype. Carriage means pneumococcal colonization. There are two sequence types (STs) spreading in a population each of which can be expressed as one of two serotypes. We derive the differential equation model for the carriage spread and perform an equilibrium and global stability analysis on it. A key parameter is the effective reproduction number R (e). For R (e) ≤ 1,  there is only the carriage-free equilibrium (CFE) and the carriage will die out whatever be the starting values. For R (e) > 1, unless the effective reproduction numbers of the two STs are equal, in addition to the CFE there are two carriage equilibria, one for each ST. If the ST with the largest effective reproduction number is initially present, then in the long-term the carriage will tend to the corresponding equilibrium.

Crowding and other strong predictors of upper respiratory tract carriage of otitis media-related bacteria in Australian Aboriginal and non-Aboriginal children

BACKGROUND

Streptococcus pneumoniae, Moraxella catarrhalis, and nontypeable Haemophilus influenzae is associated with otitis media (OM). Data are limited on risk factors for carriage of these pathogens, particularly for Indigenous populations. We investigated predictors of nasopharyngeal carriage in Australian Aboriginal and non-Aboriginal children.

METHODS

Nasopharyngeal aspirates were collected up to 7 times before age 2 years from 100 Aboriginal and 180 non-Aboriginal children. Longitudinal modeling estimated effects of environmental factors and concurrent carriage of other bacteria on the probability of bacterial carriage. We present a novel method combining the effects of number of household members and size of house into an overall crowding model.

RESULTS

Each additional household member increased the risk of carriage of S. pneumoniae (odds ratio [OR] = 1.45 per additional Aboriginal child in a 4-room house, 95% confidence interval [CI]: 1.15-1.84; OR = 2.34 per additional non-Aboriginal child, 95% CI: 1.76-3.10), with similar effect sizes for M. catarrhalis, and nontypeable Haemophilus influenzae. However, living in a larger house attenuated this effect among Aboriginal children. Daycare attendance predicted carriage of the 3 OM-associated bacteria among non-Aboriginal children. Exclusive breast-feeding at 6 to 8 weeks protected against Streptococcus aureus carriage (OR = 0.42, 95% CI: 0.19-0.90 in Aboriginal children and OR = 0.49, 95% CI: 0.25-0.96 in non-Aboriginal children). OM-associated bacteria were more likely to be present if there was concurrent carriage of the other OM-associated species.

CONCLUSIONS

This study highlights the importance of household transmission in carriage of OM bacteria, underscoring the need to reduce the crowding in Aboriginal households.

Nasopharyngeal carriage of Streptococcus pneumoniae in Taiwan before and after the introduction of a conjugate vaccine

BACKGROUND

The heptavalent pneumococcal conjugate vaccine was introduced in Taiwan in October 2005. To evaluate the effect of the vaccination, we conducted an active, prospective, large-scale, long-term, and multicenter study to assess the prevalence of nasopharyngeal Streptococcus pneumoniae carriage in Taiwanese children.

METHODS

This study was performed at three tertiary teaching hospitals in northern, central, and southern Taiwan. Questionnaires provided demographic, family/household, and medical history data. Pneumococcal isolates were tested for their susceptibility to various antimicrobial agents and serotypes. In addition, influenza virus and Staphylococcus aureus were recovered from nasopharyngeal and nasal swabs, respectively.

RESULTS

Between July 2005 and July 2008, 857 pneumococcal strains were recovered from a total of 6057 children aged >2 months to 5 years (carriage rate, 14.1%). Carriage rates differed geographically and varied with subject age. In a multivariate analysis, having at least one sibling, attendance at day-care centers, a history of otitis media, and history of upper respiratory tract infection in the previous 2 weeks were each associated with a higher risk of pneumococcal colonization of the nasopharynx. Staphylococcus aureus nasal colonization was inversely associated with nasopharyngeal carriage of pneumococcus (p=0.000; odds ratio [OR]: 0.48; 95% CI: 0.39-0.58). Daycare attendance was the only risk factor for carriage of penicillin non-susceptible S. pneumoniae (OR: 2.37; 95% CI: 1.22-4.88). Although vaccination rates rose from 2005 to 2008, no concomitant decrease in S. pneumoniae carriage occurred. The rate of penicillin resistance among S. pneumoniae isolates was 92.8% (using the meningitis criteria). The prevalence of cefotaxime resistance (21.6%) was higher than that of penicillin (6.9%; non-meningitis criteria). Slightly more than half (57.4%) of the isolates belonged to strains covered by the heptavalent pneumococcal conjugate vaccine when both vaccine and vaccine-related serotypes were included.

CONCLUSIONS

Although vaccination rates rose from 2005 to 2008, no concomitant decrease occurred in S. pneumoniae carriage. Interaction between S. aureus and S. pneumoniae may influence vaccination efficacy. These findings provide baseline data to further compare pneumococcal carriage rates and antibiotic resistance patterns in Taiwanese children as vaccination rates continue to increase.

A decade-long surveillance of nasopharyngeal colonisation with Streptococcus pneumoniae among children attending day-care centres in south-eastern France: 1999-2008

The antimicrobial resistance and serotype distribution of Streptococcus pneumoniae (SP) among children attending day-care centres in south-eastern France were monitored from 1999 to 2008, before and after interventions promoting prudent antibiotic use initiated in 2000 and the availability of pneumococcal conjugate vaccine in 2003. Antibiotic susceptibility and serotypes of SP isolates were determined on nasopharyngeal samples of children aged 3-40 months attending day-care centres, from January to March 1999, 2002, 2004, 2006 and 2008. SP carriage fell from 54% to 45%, and SP with diminished susceptibility to penicillin (PDSP) fell from 34% to 19%. Antibiotic prescriptions dropped from 63% to 38% of children, but third-generation cephalosporins were increasingly prescribed. The overall antibiotic susceptibility increased. Over 90% of the children had received at least one vaccine dose in 2008. Vaccine serotypes 6B, 9V, 19F and 23F (76%) in 1999 were replaced by non-vaccine types (95%) in 2008, among which were 15 (20%), 19A (15%), 23A/B (10%) and 6A (9%). Serotypes 6A, 19A and 15 accounted for over 50% of PDSP strains in 2008 versus 6% in 1999. Children now mostly harbour non-vaccine types; however, PDSP isolates are mainly recruited among these. Vaccine-related benefits may be threatened by combined vaccine- and antibiotic-driven selective pressure.

Sequential multiplex PCR assay for determining capsular serotypes of colonizing S. pneumoniae

Background

Asymptomatic nasopharyngeal carriage represents an important biological marker for monitoring pneumococcal serotype distribution and evaluating vaccine effects. Serotype determination by conventional method (Quellung reaction) is technically and financially challenging. On the contrary, PCR-based serotyping represents a simple, economic and promising alternative method.

Method

We designed a novel multiplex PCR assay for specific detection of the 30 classical colonizing S. pneumoniae serogroups/types. This multiplex assay is composed of 7 consecutive PCR reactions and was validated on a large and recent collection of Streptococcus pneumoniae isolated during a prospective study conducted in Belgium at the time of PCV7 adoption.

Results

The multiplex PCR assay allowed the typing of more than 94% of the isolates of a collection of pneumococci isolated from Belgian preschool attendees (n = 332). Seventy-five percent of the isolates were typed after 3 subsequent PCR reactions. Results were in agreement with the Quellung identification.

Conclusion

Our novel multiplex assay is an accurate and reliable method which can be used in place of the conventional method for S. pneumoniae carriage studies.

Probabilistic network modelling of the impact of penicillin consumption on spread of pneumococci

The worldwide increase of resistant S. pneumoniae is a growing clinical problem. In several countries, a more restrictive use of penicillin has been promoted in hope of slowing the rates of resistant pneumococci. However, the consequences of such an action on pneumococcal population dynamics are not fully understood. Thus, a network model was constructed to assess the impacts of penicillin consumption and between-strain competition on the spread of penicillin non-susceptible pneumococci. Model simulations suggest that the age distribution for carriage of penicillin non-susceptible pneumococci, in contrast to susceptible pneumococci, is affected by penicillin consumption. Furthermore, it appears extremely difficult to reduce the incidence of penicillin non-susceptible pneumococci by simply controlling penicillin consumption, assuming that reduced penicillin susceptibility does not confer a fitness cost for the organism. A more judicious use of penicillin together with control measures are in that case required to manage penicillin resistance in pneumococci.

Impact of a pneumococcal conjugate vaccination program on carriage among children in Norway

In July 2006, the seven-valent pneumococcal conjugate vaccine (PCV7) was introduced in Norway with a reduced (2 doses + 1 boost) dose schedule. Post-PCV7 shifts in pneumococcal reservoirs were assessed by two point prevalence studies of nasopharyngeal colonization among children in day care centers, before (2006) and after (2008) widespread use of PCV7. Nasopharyngeal swabs were obtained from 1,213 children, 611 in 2006 and 602 in 2008. A total of 1,102 pneumococcal isolates were recovered. Serotyping, multilocus sequence typing, and antimicrobial drug susceptibility testing were performed on all isolates. Although carriage of PCV7 serotypes decreased among both vaccinated and unvaccinated children, the overall prevalence of pneumococcal carriage remained high (80.4%) after vaccine introduction. The pneumococcal populations were diverse, and in the shift toward non-PCV7 serotypes, expansion of a limited number of established clonal complexes was observed. While non-antimicrobial-susceptible clones persisted among PCV7 serotypes, antimicrobial resistance did not increase among non-PCV7 serotypes. Direct and indirect protection of PCV7 against nasopharyngeal colonization was inferred from an overall decrease in carriage of PCV7 serotypes. No preference was found for nonsusceptible clones among the replacing non-PCV7 serotypes.

Pneumococcal serotypes causing pediatric meningitis in Turkey: application of a new technology in the investigation of cases negative by conventional culture

The surveillance of serotypes causing invasive pneumococcal disease (IPD) provides further insight into the pathogenesis of pneumococcal disease and is important in order to track vaccine impact. Although the Quellung reaction has been accepted as the standard method for serotyping, prior antibiotic use causes a gap in studies based on bacterial culture. A total of 31 cerebrospinal fluid (CSF) samples found to be positive for Streptococcus pneumoniae by polymerase chain reaction (PCR) targeting the ply gene during an active surveillance were tested in a Bio-Plex multiplex antigen detection assay capable of detecting 14 serotypes/groups (1, 3, 4, 5, 6A, 6B, 7F/A, 8, 9V, 14, 18, 19A, 19F, and 23F). Twenty-seven CSF samples could be serotyped. The most common serotypes were serotypes 5 (n = 7), 19F (n = 5), 1 (n = 3), and 23F (n = 3). Theoretical coverage rates by the heptavalent (PCV7), 10-valent (PCV10), and 13-valent (PCV13) pneumococcal conjugate vaccines for bacterial meningitis were 48.1, 85.2, and 92.3%, respectively, for all age groups and 71.4, 85.7, and 100.0%, respectively, for those under 2 years of age. We propose that antigen detection assay used in conjunction with a PCR assay can be effectively applied in CSF samples to detect the pneumococcal serotypes, especially when the patient may have already been treated and, therefore, the cultures would be negative.

Parental Staphylococcus aureus carriage is associated with staphylococcal carriage in young children

BACKGROUND

Staphylococcus aureus colonization typically precedes infection but risk factors for colonization in children are not well defined. Our previous study suggested that S. aureus carriage in children is associated with parental carriage. Here we wished to distinguish the different components that play a role in the risk to a child of a S. aureus-carrying parent.

METHODS

Between 2002 and 2005, children (0-40 months) and their parents were screened for carriage of S. aureus and Streptococcus pneumoniae during 1 of 6 surveys. Data were collected from the parents and the medical files. Multivariate analysis of possible associated factors and effect modifiers was carried out. Pulse-field gel electrophoresis was performed to determine strain relatedness.

RESULTS

A total of 4648 children were screened. S. aureus was isolated from 342 (7.6%) children and 992 (22%) parents. Pairs of parent-child carriers were found in 155 cases, over twice the rate expected by chance (1.66%, P<0.0001). The variable that was most significantly associated with carriage in children was having a parent carrier (OR: 3.35; 95% CI: 2.59-4.33), whereas close contact with peers (as assessed by day care centers attendance or having young siblings) was not associated with carriage. Children<3 months had the highest carriage rate and children aged 6 to 12 months had the lowest (25.4% and 4.3%, respectively, P<0.0001). Breast-feeding was not associated with higher or lower carriage. In 30 of 150 strains studied, >70% parent-child strains were genetically identical.

CONCLUSIONS

Parental S. aureus colonization, but not DCC attendance or having young siblings, is an independent predictor for staphylococcal carriage in young children.

Outbreaks of Streptococcus pneumoniae carriage in day care cohorts in Finland - implications for elimination of transmission

Background

Day care centre (DCC) attendees play a central role in maintaining the circulation of Streptococcus pneumoniae (pneumococcus) in the population. Exposure within families and within DCCs are the main risk factors for colonisation with pneumococcal serotypes in DCC attendees.

Methods

Transmission of serotype specific carriage was analysed with a continuous time event history model, based on longitudinal data from day care attendees and their family members. Rates of acquisition, conditional on exposure, were estimated in a Bayesian framework utilising latent processes of carriage. To ensure a correct level of exposure, non-participating day care attendees and their family members were included in the analysis. Posterior predictive simulations were used to quantify transmission patterns within day care cohorts, to estimate the basic reproduction number for pneumococcal carriage in a population of day care cohorts, and to assess the critical vaccine efficacy against carriage to eliminate pneumococcal transmission.

Results

The model, validated by posterior predictive sampling, was successful in capturing the strong temporal clustering of pneumococcal serotypes in the day care cohorts. In average 2.7 new outbreaks of pneumococcal carriage initiate in a day care cohort each month. While 39% of outbreaks were of size one, the mean outbreak size was 7.6 individuals and the mean length of an outbreak was 2.8 months. The role of families in creating and maintaining transmission was minimal, as only 10% of acquisitions in day care attendees were from family members. Considering a population of day care cohorts, a child-to-child basic reproduction number was estimated as 1.4 and the critical vaccine efficacy against acquisition of carriage as 0.3.

Conclusion

Pneumococcal transmission occurs in serotype specific outbreaks of carriage, driven by within-day-care transmission and between-serotype competition. An amplifying effect of the day care cohorts enhances the spread of pneumococcal serotypes within the population. The effect of vaccination, in addition to reducing susceptibility to pneumococcal carriage in the vaccinated, induces a herd effect, thus creating a counter-effect to the amplifying effect of the cohort. Consequently, the critical vaccine efficacy against carriage, required for elimination of transmission, is relatively low. Use of pneumococcal conjugate vaccines is expected to induce a notable herd protection against pneumococcal disease.

Transmission-dynamic model to capture the indirect effects of infant vaccination with Prevnar (7-valent pneumococcal conjugate vaccine (PCV7)) in older populations

We developed an age-structured, transmission-dynamic, mathematical model to quantify the direct and indirect benefits of infant PCV7 vaccination. The model simulates the acquisition of asymptomatic carriage of Streptococcus pneumoniae and the development of fatal and non-fatal invasive pneumococcal disease (IPD) among vaccinated and unvaccinated individuals aged <2, 2-4, 5-17, 18-49, 50-64, and >or=65 years old. The model was parameterized using published US surveillance data, supplemented with data from published literature. The model predicts the observed incidence of IPD with good agreement and may be used to predict the impact of various vaccination strategies in the US or other populations yet to introduce PCV7.

Antibiotics versus placebo or watchful waiting for acute otitis media: a meta-analysis of randomized controlled trials

BACKGROUND

Recommendations on withholding antibiotics in children with acute otitis media (AOM) have been inadequately implemented in clinical practice.

OBJECTIVES

We evaluated the role of prescribing antibiotics for AOM.

METHODS

We performed a meta-analysis of randomized controlled trials (RCTs) that were retrieved from searches performed in the PubMed and Cochrane databases, and compared antibiotic treatment with placebo or watchful waiting (delayed antibiotic treatment if clinically indicated) for patients with AOM.

RESULTS

We identified seven trials comparing antibiotic treatment with placebo (all double-blinded) and four trials comparing antibiotic treatment with watchful waiting (two investigator-blinded and two open-label) trials, all of which involved children (6 months to 12 years). Clinical success was more likely with antibiotics than comparator treatment in: placebo-controlled trials [seven RCTs, 1405 patients, risk ratio (RR) = 1.11, 95% confidence interval (CI) = 1.05-1.18]; watchful waiting trials (four RCTs, 915 patients, RR = 1.18, 95% CI = 1.07-1.32); and all trials combined (11 RCTs, 2320 patients, RR = 1.13, 95% CI = 1.08-1.19). Similarly, persistence of symptoms 2-4 days after treatment initiation was less likely with antibiotics in: placebo-controlled trials (four RCTs, 1014 patients, RR = 0.75, 95% CI = 0.64-0.88) and all trials combined (five RCTs, 1299 patients, RR = 0.68, 95% CI = 0.54-0.85). Diarrhoea was more likely with antibiotics (seven RCTs, 1807 patients, RR = 1.50, 95% CI = 1.16-1.95). No differences between the compared treatments were found regarding other effectiveness and safety outcomes.

CONCLUSIONS

Antibiotic treatment is associated with a more favourable clinical course in children with AOM, compared with placebo, and also compared with watchful waiting. However, safety issues and the rather small treatment effect difference render the consideration of additional factors necessary in relevant clinical decision making.

Changes in pneumococcal serotypes and antibiotypes carried by vaccinated and unvaccinated day-care centre attendees in Portugal, a country with widespread use of the seven-valent pneumococcal conjugate vaccine

The seven-valent pneumococcal conjugate vaccine (PCV7) has been available in Portugal since June 2001, but is not included in the National Vaccination Plan. Its impact on colonization is unknown. A point-prevalence study to evaluate PCV7 usage was carried out in 2006 among day-care centre attendees from the Lisbon area. Pneumococcal carriage rates, serotypes, and antibiotypes were determined and compared with results from a similar study conducted in 2001 before vaccine approval. In 2001 and 2006, 717 and 571 children, respectively, were enrolled. In 2006, 45.9% of the participants were appropriately vaccinated and 11.5% were incompletely vaccinated. Carriage of pneumococci remained stable (64.9% in 2001; 68.7% in 2006). Vaccine types (VT) decreased from 53.1% of all pneumococci to 11.2% (p <0.001). Serotype replacement was observed among vaccinated and unvaccinated children. Non-vaccine types (NVT) 1, 6C, 7F, 15A, 16F, 21, 23A, 29, and non-typeable (NT) strains increased significantly; serotype 19A increased, but not significantly. Rates of resistance to penicillin, erythromycin, clindamycin and tetracycline remained stable (p >0.05) due to significant increases in intermediate resistance to penicillin (from 5.5% to 17.8%), erythromycin (from 9.2% to 21.8%), clindamycin (from 6.4% to 19.3%) and tetracycline (from 8.3% to 15.8%) among NVT. Whereas in 2001 resistance among NVT was mostly associated with serotype 19A and NT strains, in 2006 resistance was also found among serotypes 6C, 15A, 24F and 33F. In conclusion, dramatic shifts in serotypes of colonizing pneumococci were observed among vaccinated and unvaccinated children. Rates of antibiotic resistance remained unchanged due to a balance between reduction in VT and an increase in antimicrobial-resistant NVT.

Clustering of serotypes in a longitudinal study of Streptococcus pneumoniae carriage in three day care centres

BACKGROUND

Streptococcus pneumoniae (pneumococcus) causes a wide range of clinical manifestations that together constitute a major burden of disease worldwide. The main route of pneumococcal transmission is through asymptomatic colonisation of the nasopharynx. Studies of transmission are currently of general interest because of the impact of the new conjugate-polysaccharide vaccines on nasopharyngeal colonisation (carriage). Here we report the first longitudinal study of pneumococcal carriage that records serotype specific exposure to pneumococci simultaneously within the two most important mixing groups, families and day care facilities.

METHODS

We followed attendees (N = 59) with their family members (N = 117) and the employees (N = 37) in three Finnish day care centres for 9 months with monthly sampling of nasopharyngeal carriage. Pneumococci were cultured, identified and serotyped by standard methods.

RESULTS

Children in day care constitute a core group of pneumococcal carriage: of the 36 acquisitions of carriage with documented exposure to homologous pneumococci, the attendee had been exposed in her/his day care centre in 35 cases and in the family in 9 cases. Day care children introduce pneumococci to the family: 66% of acquisitions of a new serotype in a family were associated with simultaneous or previous carriage of the same type in the child attending day care. Consequently, pneumococcal transmission was found to take place as micro-epidemics driven by the day care centres. Each of the three day care centres was dominated by a serotype of its own, accounting for 100% of the isolates of that serotype among all samples from the day care attendees.

CONCLUSION

The transmission of pneumococci is more intense within than across clusters defined by day care facilities. The ensuing micro-epidemic behaviour enhances pneumococcal transmission.

The association between antibiotic use in the community and nasopharyngeal carriage of antibiotic-resistant Streptococcus pneumoniae in Bedouin children

BACKGROUND

The objective of the study was to evaluate whether the increase in antibiotic-resistant Streptococcus pneumoniae carriage was associated with antibiotic use in the community in children in Southern Israel.

METHODS

All the prescriptions given to Bedouin children <5 years old enlisted in 2 sentinel primary pediatric clinics treating approximately 20% of the Bedouin pediatric population of this age range were recorded, from 1998 to 2005. Nasopharyngeal pneumococcal isolates obtained during the same period from healthy children <5 years old were collected and antibiotic susceptibility was determined.

RESULTS

A total of 1488 of 1927 (77.7%) cultures were positive for S. pneumoniae. The proportion of S. pneumoniae with penicillin minimal inhibitory concentration > or = 1.0 microg/mL increased from 8% to 21% (P < 0.01); resistance to clindamycin from 9% to 22%; resistance to erythromycin from 13% to 30%; resistance to tetracycline from 13% to 31%; and multidrug resistance from 16% to 30%. The total annual antibiotic prescription rates decreased by 19%, from 3867 to 3191 prescriptions per 1000 children (P < 0.001). This was mainly the result of a reduction in amoxicillin +/- clavulanate prescriptions (from 3046 to 2582; P < 0.001). Oral cephalosporin, erythromycin and penicillin prescription rates decreased significantly as well (P < 0.001) whereas azithromycin prescription rates increased significantly (P < 0.001).

CONCLUSIONS

We suggest that the increased carriage of S. pneumoniae resistant to multiple antibiotics is possibly associated to the increased azithromycin consumption. Reduction of total antibiotic use may not be sufficient as long as antibiotics with high potential to promote multidrug resistance, given their pharmacokinetics and pharmacodynamics characteristics, are widely used.

Acute otitis media in children: association with day care centers--antibacterial resistance, treatment, and prevention

Children attending day care centers (DCCs) frequently carry antibacterial-resistant organisms in their nasopharynx, leading to acute otitis media (AOM) that may be refractory to antibacterial treatment. The development and spread of resistant organisms are facilitated in DCCs as a result of the following: (i) large numbers of children; (ii) frequent close person-to-person contact; and (iii) a wide use of antimicrobial medications. Intensive antimicrobial usage provides the selection pressure that favors the emergence of resistant organisms, while DCCs provide an ideal environment for transmission of these organisms. The American Academy of Pediatrics and American Academy of Family Physicians' guidelines recommend high-dose amoxicillin/clavulanic acid (rather than amoxicillin alone) as the first therapeutic choice in the treatment of AOM in children attending DCCs. The introduction of the 7-valent pneumococcal conjugated vaccine (PCV7) had a major role in decreasing the number of episodes of Streptococccus pneumoniae AOM secondary to the serotypes included in the vaccine. It also had a major role in reducing the nasopharyngeal carriage of vaccine-type S. pneumoniae (and in particular of antibacterial-resistant organisms), preventing, in this way, its spread to contacts in the community. However, the recent observation of increased rates of antibacterial-resistant non-vaccine serotype S. pneumoniae may erode the success of PCV7.

Use of antibiotics and risk factors for carriage of Streptococcus pneumoniae: a longitudinal household study in the United Kingdom

This study aimed to identify risk factors and assess the impact of coincidental antibiotic therapy on carriage of Streptococcus pneumoniae. Index children from birth to 3 years and their households were recruited from primary health-care registers in four UK general practices. Nasopharyngeal swabs were taken monthly from study participants ten times between October 2001 and July 2002. Multilevel random-effect models were used to adjust for statistical dependence between repeated measurements and family clustering of carriage. Carriage results were available for 3753 swabs from 489 individuals in 121 families. Crude prevalence of carriage was 25%. On multivariable analysis, risk of carriage was reduced by antibiotic use the previous month [odds ratio (OR) 0.34, 95% confidence interval (CI) 0.22-0.52], but increased if a child attended day care for >20 h per week (OR 2.52, 95% CI 1.41-4.52). Taking antibiotics significantly reduces the risk of carriage the following month in a setting with a low prevalence of pneumococcal antimicrobial resistance.

Transmission of Streptococcus pneumoniae in an urban slum community

BACKGROUND

Inhabitants of slum settlements represent a significant proportion of the population at risk for pneumococcal disease in developing countries.

METHODS

We conducted a household survey of pneumococcal carriage among residents of a slum community in the city of Salvador, Brazil.

RESULTS

Among 262 subjects, 95 (36%) were colonized with Streptococcus pneumoniae. Children <5 years of age (OR, 8.0; 95% CI, 3.5-18.6) and those who attended schools (OR, 2.7, 95% CI, 1.2-6.0) had significantly higher risk of being colonized. Of 94 isolates obtained from colonized individuals, 51% had serotypes included in the seven-valent pneumococcal conjugate vaccine. Overall, 10% (9 of 94 isolates) were nonsusceptible to penicillin and 28% (27 of 94 isolates) were resistant to cotrimoxazole. BOX-PCR, PFGE and MLST analyses found that 44% of the carriage isolates belonged to 14 distinct clonal groups. Strains of the same clonal group were isolated from multiple members of 9 out of the 39 study households. Nineteen carriage isolates had genotypes that were the same as those identified among 362 strains obtained from active surveillance for meningitis.

CONCLUSIONS

The study's findings indicate that there is significant intra- and inter-household spread of S. pneumoniae in the slum community setting. However, a limited number of clones encountered during carriage among slum residents were found to cause invasive disease.

An individual-based network model to evaluate interventions for controlling pneumococcal transmission

Background

Streptococcus pneumoniae is a major cause of morbidity and mortality worldwide, but also a common colonizer of the upper respiratory tract. The emergence and spread of antibiotic resistant pneumococcal strains has threatened effective therapy. The long-term effects of measures aiming to limit pneumococcal spread are poorly understood. Computational modeling makes it possible to conduct virtual experiments that are impractical to perform in real life and thereby allows a more full understanding of pneumococcal epidemiology and control efforts.

Methods

We have developed a contact network model to evaluate the efficacy of interventions aiming to control pneumococcal transmission. Demographic data from Sweden during the mid-2000s were employed. Analyses of the model's parameters were conducted to elucidate key determinants of pneumococcal spread. Also, scenario simulations were performed to assess candidate control measures.

Results

The model made good predictions of previous findings where a correlation has been found between age and pneumococcal carriage. Of the parameters tested, group size in day-care centers was shown to be one of the most important factors for pneumococcal transmission. Consistent results were generated from the scenario simulations.

Conclusion

We recommend, based on the model predictions, that strategies to control pneumococcal disease and organism transmission should include reducing the group size in day-care centers.

Valuing reduced antibiotic use for pediatric acute otitis media

OBJECTIVE

The 2004 American Academy of Pediatrics acute otitis media guidelines urge parents to weigh the benefits of reduced antibiotic use, adverse drug events, and future resistance versus risks of extra costs and sick days resulting from guideline use. The value of decreased antibiotic resistance has not been quantified. The objective was to perform cost-utility analysis, estimating the resistance value of implementing the guidelines for acute otitis media treatment for children <2 years of age. Outcomes were described with a common denominator and the value of avoiding resistance was estimated using a parental perspective.

METHODS

Decision analysis results were used for outcome probabilities. Published utilities were used to describe outcomes in quality-adjusted life-day units. The minimum resistance benefit value, where the benefits of the American Academy of Pediatrics guidelines would at least balance their costs, was defined as the guidelines' incremental costs minus their other benefits.

RESULTS

For a child 2 to <6 months of age presenting to a primary care physician with possible otitis media, parents would need to value the resistance benefit at 0.77 quality-adjusted life-days per antibiotic prescription avoided for the guidelines' benefits to balance their costs. For the 6- to <24-month-old group, results were 0.67 quality-adjusted life-days per prescription avoided. Results were sensitive to the dollar cost utility; when willingness to pay ranged from $20,000 to $200,000 per quality-adjusted life-year, results ranged from 0.36 and 0.30 quality-adjusted life-days up to 4.10 and 3.57 quality-adjusted life-days for the 2- to <6-month-old and 6- to <24-month-old groups, respectively. Costs were driven by missed parent work days.

CONCLUSIONS

From a societal perspective, trading 0.30 to 4 quality-adjusted life-days to avoid 1 antibiotic course might be desirable; from a parental perspective, this may not be as desirable. Parent demand for antibiotics may be rational when driven by the value of parent time. Other approaches that have the potential to reduce antibiotic use, such as wider use of influenza vaccine and improved rapid viral diagnostic techniques, might be more successful.

High rates of transmission of and colonization by Streptococcus pneumoniae and Haemophilus influenzae within a day care center revealed in a longitudinal study

Day care centers (DCCs) are unique settings where young children are at increased risk for colonization by pneumococci and Haemophilus influenzae. Although point prevalence studies in DCCs are frequent, only a few longitudinal studies on the dynamics of colonization have been published. We conducted a 1-year longitudinal study with 11 sampling periods on nasopharyngeal carriage of pneumococci and H. influenzae among 47 children who attended a single DCC. All isolates were antibiotyped and genotyped by pulsed-field gel electrophoresis. Pneumococci were also serotyped. Of the 414 samples obtained, 61.4% contained pneumococci, and 87% contained H. influenzae. Only 8.3% of the samples were negative for both species. Twenty-one pneumococcal clones and 47 H. influenzae clones were identified. Introduction of clones occurred during all year. Ninety-eight percent and 96% of all pneumococcal and H. influenzae isolates, respectively, belonged to clones shared by more than one child. Children were sequentially colonized with up to six pneumococcal clones (mean, 3.6) and five serotypes and nine H. influenzae clones (mean, 7.1). Clones with increased capacity for transmission and/or prolonged colonization were identified in both species. These two fitness properties appeared to be independent. In conclusion, among DCC attendees, a high rate of acquisition and turnover of strains was observed, and all children were overwhelmingly colonized by clones shared with others. DCCs are units where permanent introduction of new clones occurs, and attendees, as a whole, provide a pool of hosts where the fittest clones find privileged opportunities to persist and expand.

Pneumococcal carriage among indigenous Warao children in Venezuela: serotypes, susceptibility patterns, and molecular epidemiology

Little attention has been paid to pneumococcal carriage and disease in Amerindians from Latin America. The Warao people, an indigenous population from Venezuela, live in the delta of the Orinoco River in geographically isolated communities with difficult access to medical care. To obtain insight into pneumococcal carriage and the theoretical coverage of pneumococcal vaccines in this population, we investigated pneumococcal colonization, serotype, and genotype distribution among Warao children in 9 distinct, geographically isolated communities in the Delta Amacuro area in the northeast of Venezuela. From April 2004 through January 2005, a total of 161 Streptococcus pneumoniae isolates were recovered from single nasopharyngeal swab samples obtained from 356 children aged 0-72 months. The overall pneumococcal carriage rate was 49%, ranging from 13% to 76%, depending on the community investigated and the age of the children (50% among children aged <2 years and 25% among children aged >2 years). The most frequent serotypes were 23F (19.5% of isolates), 6A (19.5%), 15B (10.4%), 6B (9.1%), and 19F (7.2%). The theoretical coverage of the 7-valent pneumococcal conjugate vaccine, including the cross-reactive nonvaccine serotype 6A, was 65%. A total of 26% of the isolates were resistant to first-line antibiotics, with 70% of these strains being covered by the 7-valent pneumococcal conjugate vaccine. Restriction fragment end labelling analysis revealed 65 different genotypes, with 125 (80%) of the isolates belonging to 27 different genetic clusters, suggesting a high degree of horizontal spread of pneumococcal strains in and between the villages. The high colonization rates and high (registered) acute respiratory tract infection morbidity and mortality in this part of Venezuela suggest that Warao children are at increased risk for pneumococcal disease and, therefore, benefit from vaccination.

Social mixing with other children during infancy enhances antibody response to a pneumococcal conjugate vaccine in early childhood

Children who have siblings and/or who attend day care have higher rates of nasopharyngeal colonization with pneumococci than lone children do. Pneumococcal colonization is usually asymptomatic but is a prerequisite for invasive disease. We studied the effect of social mixing with other children on immunity to a pneumococcal vaccine. One hundred sixty children aged 1 year were immunized with a 7-valent conjugate pneumococcal vaccine. A blood sample was obtained before and 9 to 11 days after the vaccine. The concentration and avidity of antibody against vaccine pneumococcal serotypes (4, 6B, 9V, 14, 18C, 19F, and 23F) were studied in relation to pneumococcal carriage rate and measures of social mixing. Children with increased social mixing had higher antibody concentrations against serotypes 4, 9V, 14, and 23F than lone children did. The least-carried serotype, serotype 4, was the one of the most immunogenic. This contrasts with serotype 6B, the most common nasopharyngeal isolate but the least immunogenic. Social mixing in infancy enhances the immune response to a Streptococcus pneumoniae polysaccharide-protein conjugate vaccine at 1 year of age. Exposure to pneumococci in the first year of life may induce immunological priming. An alternative explanation is that differences in immunological experience, such as increased exposure to respiratory viral infections in early childhood, alters the response to vaccines perhaps by affecting the balance between Th1 and Th2 cytokines. The low immunogenicity of serotype 6B polysaccharide might make conditions more favorable for carriage of the 6B organism and explain why 6B pneumococci were more frequently isolated than other serotypes.

Empiric first-line antibiotic treatment of acute otitis in the era of the heptavalent pneumococcal conjugate vaccine

OBJECTIVES

Our goal was to estimate the local prevalence of Streptococcus pneumoniae nonsusceptible to penicillin and amoxicillin after widespread use of the heptavalent pneumococcal vaccine and to revise community-specific recommendations for first-line antibiotic treatment of acute otitis media.

METHODS

We conducted serial prevalence surveys between 2000 and 2004 in the offices of community pediatricians in St Louis, Missouri. Study participants were children <7 years of age with acute upper respiratory infections. Children treated with an antibiotic in the past 4 weeks were excluded. S pneumoniae was isolated from nasopharyngeal swabs using standard techniques. Isolates with a penicillin minimum inhibitory concentration >2 microg/mL were considered to be S pneumoniae nonsusceptible to amoxicillin.

RESULTS

There were 327 patients enrolled in the study. Between 2000 and 2004, vaccine coverage with > or =3 doses of heptavalent pneumococcal vaccine increased from 0% to 54%, but nasopharyngeal carriage of S pneumoniae was stable at 39%. The prevalence of S pneumoniae nonsusceptible to penicillin fell from 25% to 12% among patients, did not vary if <2 years of age, was reduced in children with > or =3 doses of heptavalent pneumococcal vaccine, and increased in child care attendees but reduced in attendees who had > or =3 doses of heptavalent pneumococcal vaccine. The prevalence of S pneumoniae nonsusceptible to amoxicillin in patients remained <5%.

CONCLUSIONS

In our community, widespread use of heptavalent pneumococcal vaccine has reduced the prevalence of S pneumoniae nonsusceptible to penicillin, and the prevalence of S pneumoniae nonsusceptible to amoxicillin remains low (<5%). If antibiotic treatment is elected for children with uncomplicated acute otitis media, we recommend treatment with standard-dose amoxicillin (40-45 mg/kg per day) for children with > or =3 doses of heptavalent pneumococcal vaccine, regardless of age and child care status. High-dose amoxicillin should be used for children with <3 doses of heptavalent pneumococcal vaccine and those treated recently with an antibiotic.