Hotspot or blind spot? Fine-scale spatial heterogeneity and methodological bias in Chlamydia psittaci prevalence rate reports from urban feral pigeons (Columba livia f. urbana).

Urban wildlife populations often carry zoonotic pathogens that pose considerable public health risks through direct contact with humans. However, disease prevalence in urban settings is generally reported at the city level, which disregards spatial heterogeneity due to local differences in habitat structure or resource availability in the urban landscape. This study therefore examines the fine-scale spatial heterogeneity of Chlamydia psittaci, a generalist bacterium that frequently infects feral pigeons, in Antwerp, Belgium. We collected samples from 377 pigeons at 23 locations and performed qPCR screening for C. psittaci. At the same time, we performed an extensive literature review that includes 20 studies from 29 unique cities globally. Our findings indicate that the prevalence variance within Antwerp (CV = 0.70) is comparable to the variation reported among cities worldwide (CV = 0.88), suggesting that distinct locations within a single city can exhibit differences comparable to those between entirely different cities. Our data suggest that citywide or even countrywide are likely confounded by small scale spatial infection heterogeneity. A combination simulation showed that at least 12 unique sampling sites are necessary to accurately assess the true prevalence at the city level. Finally, we could show that also the screening method influences reported prevalence, with blood samples and non-PCR screening inflating reported prevalence rates. Taken together, we recommend that urban surveillance reports include at least 12 sampling sites, use standardized screening protocols and provide site-level data so that fine-scale heterogeneity can be taken into account.

城市野生动物种群常携带人畜共患病原体，通过与人类直接接触构成显著的公共健康风险。然而当前城市环境中的疾病流行率通常以城市为单位进行报告，忽略了城市景观中栖息地结构或资源可获得性的本地差异所导致的空间异质性。为此，本研究针对比利时安特卫普市的鹦鹉热衣原体（Chlamydia psittaci）——一种常感染野生鸽类的泛宿主细菌——的精细尺度空间异质性展开调查。我们在23个采样点采集了377只鸽类的样本，并针对鹦鹉热衣原体开展了定量聚合酶链反应（qPCR）筛查。与此同时，我们开展了全面的文献综述，纳入了全球29个独立城市的20项相关研究。研究结果显示，安特卫普市内的流行率变异系数（CV=0.70）与全球各城市间的变异系数（CV=0.88）相当，这表明单个城市内的不同区域之间的差异，可与完全不同城市之间的差异相提并论。我们的数据表明，以城市乃至国家为单位的流行率统计，很可能会因小尺度的空间感染异质性而产生混杂偏差。联合模拟分析结果显示，若要准确评估城市层面的真实流行率，至少需要设置12个独立采样点。此外，我们还证实筛查方法会对报告的流行率产生影响：血液样本检测与非聚合酶链反应筛查会高估报告的流行率数值。综上，我们建议城市野生动物疾病监测报告至少设置12个采样点、采用标准化筛查流程，并提供点位层面的采样数据，以便纳入精细尺度的空间异质性因素。