Kenya Medical Research Institute-Wellcome Trust Research Programme, Kilifi, Kenya.
J Infect Dis. 2012 Oct 1;206(7):1020-9. doi: 10.1093/infdis/jis447. Epub 2012 Jul 24.
To understand and model the impact of pneumococcal conjugate vaccines at the population level, we need to know the transmission dynamics of individual pneumococcal serotypes. We estimated serotype-specific clearance and acquisition rates of nasopharyngeal colonization among Kenyan children.
Children aged 3-59 months who were identified as carriers in a cross-sectional survey were followed-up approximately 1, 2, 4, 8, 16, and 32 days later and monthly thereafter until culture of 2 consecutive swabs yielded an alternative serotype or no pneumococcus. Serotype-specific clearance rates were estimated by exponential regression of interval-censored carriage durations. Duration was estimated as the reciprocal of the clearance rate, and acquisition rates were estimated on the basis of prevalence and duration, assuming an equilibrium state.
Of 2840 children sampled between October 2006 and December 2008, 1868 were carriers. The clearance rate was 0.032 episodes/day (95% confidence interval [CI], .030-.034), for a carriage duration of 31.3 days, and the rate varied by serotype (P< .0005). Carriage durations for the 28 serotypes with ≥ 10 carriers ranged from 6.7 to 50 days. Clearance rates increased with year of age, adjusted for serotype (hazard ratio, 1.21; 95% CI, 1.15-1.27). The acquisition rate was 0.061 episodes/day (95% CI, .055-.067), which did not vary with age. Serotype-specific acquisition rates varied from 0.0002 to 0.0022 episodes/day. Serotype-specific acquisition rates correlated with prevalence (r=0.91; P< .00005) and with acquisition rates measured in a separate study involving 1404 newborns in Kilifi (r=0.87; P< .00005).
The large sample size and short swabbing intervals provide a precise description of the prevalence, duration, and acquisition of carriage of 28 pneumococcal serotypes. In Kilifi, young children experience approximately 8 episodes of carriage per year. The declining prevalence with age is attributable to increasing clearance rates.
为了在人群层面上理解和模拟肺炎球菌结合疫苗的影响，我们需要了解个体肺炎球菌血清型的传播动态。我们估计了肯尼亚儿童鼻咽定植中血清型特异性清除和获得率。
在一项横断面调查中，被确定为带菌者的 3-59 月龄儿童在大约 1、2、4、8、16 和 32 天后以及此后每月进行随访，直到连续两次拭子培养出替代血清型或无肺炎球菌为止。通过对间隔时间进行校正的携带时间进行指数回归来估计血清型特异性清除率。持续时间被估计为清除率的倒数，并且基于患病率和持续时间来估计获得率，假设处于平衡状态。
在 2006 年 10 月至 2008 年 12 月之间采集的 2840 名儿童中，有 1868 名是带菌者。清除率为 0.032 例/天（95%置信区间 [CI]，0.030-0.034），持续时间为 31.3 天，且血清型不同（P<0.0005）。28 种血清型中，携带率≥10 的儿童的携带持续时间为 6.7 至 50 天。携带持续时间随年龄的增加而增加，经血清型调整后（危险比，1.21；95% CI，1.15-1.27）。获得率为 0.061 例/天（95% CI，0.055-0.067），与年龄无关。血清型特异性获得率从 0.0002 至 0.0022 例/天不等。血清型特异性获得率与流行率（r=0.91；P<0.00005）和在基利菲涉及 1404 名新生儿的另一项研究中测量的获得率（r=0.87；P<0.00005）相关。
大样本量和短的拭子间隔提供了对 28 种肺炎球菌血清型的流行率、持续时间和携带获得的精确描述。在基利菲，幼儿每年经历大约 8 次携带。随年龄下降的流行率归因于清除率的增加。
