Burden of Invasive Nontyphoidal Salmonella Disease in a Rural and Urban Site in Kenya, 2009–2014

Background. Invasive infections with nontyphoidal Salmonella (NTS) lead to bacteremia in children and adults and are an important cause of illness in Africa; however, few data on the burden of NTS bacteremia are available. We sought to determine the burden of invasive NTS disease in a rural and urban setting in Kenya. Methods. We conducted the study in a population-based surveillance platform in a rural setting in western Kenya (Lwak), and an informal urban settlement in Nairobi (Kibera) from 2009 to 2014. We obtained blood culture specimens from participants presenting with acute lower respiratory tract illness or acute febrile illness to a designated outpatient facility in each site, or any hospital admission for a potentially infectious cause (rural site only). Incidence was calculated using a defined catchment population and adjusting for specimen collection and healthcare-seeking practices. Results. A total of 12 683 and 9524 blood cultures were analyzed from Lwak and Kibera, respectively. Of these, 428 (3.4%) and 533 (5.6%) grew a pathogen; among those, 208 (48.6%) and 70 (13.1%) were positive for NTS in Lwak and Kibera, respectively. Overall, the adjusted incidence of invasive NTS disease was higher in Lwak (839.4 per 100 000 person-years of observation [PYO]) than in Kibera (202.5 per 100 000 PYO). The highest adjusted incidences were observed in children <5 years of age (Lwak 3914.3 per 100 000 PYO and Kibera 997.9 per 100 000 PYO). The highest adjusted annual incidence was 1927.3 per 100 000 PYO (in 2010) in Lwak and 220.5 per 100 000 PYO (in 2011) in Kibera; the lowest incidences were 303.3 and 62.5 per 100 000 PYO, respectively (in 2012). In both sites, invasive NTS disease incidence generally declined over the study period. Conclusions. We observed an extremely high burden of invasive NTS disease in a rural area of Kenya and a lesser, but still substantial, burden in an urban slum. Although the incidences in both sites declined during the study period, invasive NTS infections remain an important cause of morbidity in these settings, particularly among children <5 years old.