Use of population-based surveillance to define the high incidence of shigellosis in an urban slum in Nairobi, Kenya.

BACKGROUND: Worldwide, Shigella causes an estimated 160 million infections and >1 million deaths annually. However, limited incidence data are available from African urban slums. We investigated the epidemiology of shigellosis and drug susceptibility patterns within a densely populated urban settlement in Nairobi, Kenya through population-based surveillance. METHODS: Surveillance participants were interviewed in their homes every 2 weeks by community interviewers. Participants also had free access to a designated study clinic in the surveillance area where stool specimens were collected from patients with diarrhea (≥3 loose stools within 24 hours) or dysentery (≥1 stool with visible blood during previous 24 hours). We adjusted crude incidence rates for participants meeting stool collection criteria at household visits who reported visiting another clinic. RESULTS: Shigella species were isolated from 262 (24%) of 1,096 stool specimens [corrected]. The overall adjusted incidence rate was 408/100,000 person years of observation (PYO) with highest rates among adults 34-49 years old (1,575/100,000 PYO). Isolates were: Shigella flexneri (64%), S. dysenteriae (11%), S. sonnei (9%), and S. boydii (5%). Over 90% of all Shigella isolates were resistant to trimethoprim-sulfamethoxazole and sulfisoxazole. Additional resistance included nalidixic acid (3%), ciprofloxacin (1%) and ceftriaxone (1%). CONCLUSION: More than 1 of every 200 persons experience shigellosis each year in this Kenyan urban slum, yielding rates similar to those in some Asian countries. Provision of safe drinking water, improved sanitation, and hygiene in urban slums are needed to reduce disease burden, in addition to development of effective Shigella vaccines

Proportions of patients meeting the case definitions providing stool sample by age category.

<p>Proportions of patients meeting the case definitions providing stool sample by age category.</p

Demographic and clinical characteristics associated with shigellosis on bivariate and multivariate analysis among patients seen in study clinic, 1^st Jan 2007 to 31^st Dec 2011, Kibera.

*<p>Significant variables on bivariate analysis included into multivariate model</p>**<p>Significant characteristics on bivariate analysis but not significant on multivariate model hence excluded from final multivariate model</p

Drug susceptibility patterns for <i>Shigella</i> isolated, Kibera, Kenya.

*<p>low denominator due to stock out of Amoxicillin/clavulanic acid disks</p><p> `40 isolates did not have drug susceptibility tests done as antibiotics were not available when they were being tested</p

Person years of observation, crude and adjusted incidence of <i>Shigella</i> by age category, sex, zone and year, 1 May 2008 to 31 Dec 2010, Kibera, Kenya.

*<p>Adjusted incidence rates by zone not shown</p

Formula for adjusted incidence rate calculations.

<p>Formula for adjusted incidence rate calculations.</p

Flow chart illustrating distribution of diarrhea cases and shigella species isolated between 1 Jan 2007 and 31 Dec 2010 in Kibera, Kenya.

<p>Flow chart illustrating distribution of diarrhea cases and shigella species isolated between 1 Jan 2007 and 31 Dec 2010 in Kibera, Kenya.</p