The influence of neighbourhood on STI (and more particularly Chlamydia) acquisition is widely recognized fact.  Biello & Nikkolai argue for UK urban populations that neighbourhood socio-economic status (SES) is more closely correlated with Chlamydia risk than individual SES (http://sti.bmj.com/content/87/7/560.abstract?sid=88b6a7a5-11c9-472d-bd9a-39664d4142b7).  In another UK study (Birmingham), Shahmanesh & Ross find residence in neighbourhoods having certain SES characteristics to be  strongly predictive of both Chlamydia and Gonorrhoea (http://sti.bmj.com/content/76/4/268.abstract?sid=88b6a7a5-11c9-472d-bd9a-39664d4142b7).

But what is it exactly about these neighbourhoods that places their residents at far greater risk of STI acquisition than other neighbourhoods?  Is it, as some sociologists have proposed, the general level of social disorganization that heightens the risk, or is it poverty itself, or maybe the degree of residential instability?  Ford & Browning, in a recent study using data on a sample of 11,460 young adults from the US National Longitudinal Study of Adolescent Health, waves 1 and 3 (1994-2002), attempt to establish the pathway whereby neighbourhood influences the risk of acquiring Chlamydia (http://link.springer.com/article/10.1007%2Fs11524-013-9792-0).

The nature of the data allows the researchers to capture the association of Chlamydia acquisition amongst young people in their twenties, not only to various characteristics of their current neighbourhoods (i.e. at wave 3 of the study), but also the characteristics of those neighbourhoods in which they accomplished their transition into adulthood some years before (i.e. at wave 1).  The main finding of Ford & Browning is that characteristics of the current neighbourhood show no statistically significant correlation with Chlamydia acquisition, but characteristics of neighbourhoods at the time of adolescence – especially  “poverty” (on different models OR 1.23 & 1.25 respectively) – do show a correlation.  The obvious explanation is that these associations are mediated through individual variables such as sexual behaviour or psychological factors (e.g. depression).  Yet multi-variate findingsdid not confirm this mediation.

So what potential mechanisms are there for the influence of neighbourhood on STI acquisition?  While stressing the need for further research, the authors point principally to two.  The first of these is a “network” explanation.  Maybe neighbourhood of residence during adolescence could influence opportunities for future partner selection;  young adults who lived in an impoverished neighbourhood during adolescence may have a pool of higher risk sexual partners to choose from compared to their peers from more advantaged neighbourhoods.  The other interesting possibility is the influence of chronic stress associated with adverse neighbourhood conditions resulting in impaired immune system function and increased infectious disease risk through increased inflammation and cortisol secretion.

Either way, structural factors that are largely refractory even to the most ambitious public health interventions.  I am reminded of Wilkinson and Picket’s argument in The Spirit Level (http://www.amazon.com/The-Spirit-Level-Equality-Societies/dp/1608193411): the determinants of health outcomes are effectively located at a level that is presumably beyond of the reach of any but the most radical (indeed revolutionary) political interventions.  “The poor you will always with you.”  At the same time, sociological explanations of this kind provide justification for careful targeting of public health resources on needy populations and help us counter the “inverse care” law.