Abstract
BackgroundHigh rates of typhoid fever in children in urban settings in Asia have led to focus on childhood immunization in Asian cities, but not in Africa, where data, mostly from rural areas, have shown low disease incidence. We set out to compare incidence of typhoid fever in a densely populated urban slum and a rural community in Kenya, hypothesizing higher rates in the urban area, given crowding and suboptimal access to safe water, sanitation and hygiene.MethodsDuring 2007-9, we conducted population-based surveillance in Kibera, an urban informal settlement in Nairobi, and in Lwak, a rural area in western Kenya. Participants had free access to study clinics; field workers visited their homes biweekly to collect information about acute illnesses. In clinic, blood cultures were processed from patients with fever or pneumonia. Crude and adjusted incidence rates were calculated.ResultsIn the urban site, the overall crude incidence of Salmonella enterica serovar Typhi (S. Typhi) bacteremia was 247 cases per 100,000 person-years of observation (pyo) with highest rates in children 5–9 years old (596 per 100,000 pyo) and 2–4 years old (521 per 100,000 pyo). Crude overall incidence in Lwak was 29 cases per 100,000 pyo with low rates in children 2–4 and 5–9 years old (28 and 18 cases per 100,000 pyo, respectively). Adjusted incidence rates were highest in 2–4 year old urban children (2,243 per 100,000 pyo) which were >15-fold higher than rates in the rural site for the same age group. Nearly 75% of S. Typhi isolates were multi-drug resistant.ConclusionsThis systematic urban slum and rural comparison showed dramatically higher typhoid incidence among urban children <10 years old with rates similar to those from Asian urban slums. The findings have potential policy implications for use of typhoid vaccines in increasingly urban Africa.
Highlights
With improvements in municipal drinking water treatment, sanitation, hygiene, and food production and preparation, illness and death from typhoid fever, once rampant in New York, London and other Western cities in the late 18009s [1,2,3], became rare in industrialized nations during the 20th Century [2,3,4]
Most recent focus on typhoid disease burden has been on Asian urban centers, where high incidence rates have been documented within urban slums [5,6]
Since 2006, we have collected population-based surveillance data for infectious disease syndromes in an urban informal settlement and from a rural area in Kenya to provide data for use in characterizing emerging pathogens, estimating disease burden, defining priorities for public health research and interventions, and for sites to evaluate the impact of new interventions [8,9]
Summary
The Kenya Medical Research Institute-Centers for Disease Control and Prevention collaboration (KEMRI-CDC) has conducted active population-based surveillance for febrile illness, pneumonia, diarrheal disease and jaundice within two of 12 neighborhoods or ‘‘villages’’ in Kibera, Nairobi, Kenya and in Lwak in rural western Kenya within a district currently known as Rarieda in Nyanza Province, since October 2005 (Figure 1). The first adjustment (Adjustment #1) was based on patients who visited the study clinic and did not have a blood culture done, despite meeting fever and respiratory case definitions—this took into account that in Lwak only the first two children ,5 and the first two participants $5 years old with documented fever underwent blood culture—the adjustment put the number of people who met surveillance criteria for blood culture in the denominator and the number of patients who had blood culture done in the numerator; we divided number of participants with febrile illness criteria and ALRI criteria who had blood culture obtained by number of all surveillance participants presenting to study clinic meeting those criteria.
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