Typhi infection in Mukuru were multiple but were predominantly associated with contaminated water sources and sanitation issues Mbae et al., 2020. Typhi infections among 16,236 children was 1.4% (CI: 1.2–1.6%), and higher amongst males (1.8% vs 1.2% for females), with a high proportion of infections noted among older children 5–8 years in age Mbae et al., 2020. Over the past 7 years, we have been intensively studying typhoid and other invasive bacterial diseases in Mukuru, an informal settlement 15 km east of the city of Nairobi, Kenya.
Typhi isolates were not characterised genetically and the role of asymptomatic carriers in transmission dynamics of typhoid in the community is still poorly understood. We have previously observed carriage rates of 6% in households where typhoid cases were detected Kariuki et al., 2010, however these S. Two H58 lineages were detected lineage I being isolated between 19 and lineage II from 2004 onwards. Typhi we have characterised since 2001 Kariuki et al., 2010. Typhi H58 gained a foothold in Kenya in the 1990s, constituting >75% of the circulating S.
For the last two decades, the majority of cases of typhoid in Kenya have been MDR, with reduced susceptibility to fluoroquinolones rising in frequency Kariuki et al., 2010 Park et al., 2018 Mutai et al., 2018. The incidence of typhoid in one such informal settlement, Kibera in Nairobi, was estimated at 247 cases per 100,000 with the highest rates in children 5–9 years old (596 per 100,000) Breiman et al., 2012. In Kenya, the rapid growth of population has led to a huge rural-to-urban migration with people increasingly living in informal settlements where clean water and good sanitation are a major challenge Kyobutungi et al., 2008 Mberu et al., 2016. Recent reports of epidemics of typhoid fever in SSA suggest that the disease may be becoming more widespread in the region Crump and Mintz, 2010 Park et al., 2018 Hendriksen et al., 2015 Lutterloh et al., 2012 Marks et al., 2017 Neil et al., 2012. Typhi are rapidly displacing other lineages in many endemic areas Wong et al., 2015 Feasey et al., 2015 Kariuki et al., 2010 Park et al., 2018 and a new subclade that is extensively drug resistant (XDR), displaying resistance to ciprofloxacin and fluoroquinolones in addition to MDR, has been described in Pakistan Klemm et al., 2018. Typhi H58 Wong et al., 2015 is a globally disseminated clade frequently associated with MDR (defined as resistance to chloramphenicol, ampicillin and co-trimoxazole) and an increasing frequency of reduced susceptibility to fluoroquinolones. In this study, an estimated 45–95% of typhoid transmission was attributed to carriers Pitzer et al., 2015 Saad et al., 2017.
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Typhi and/or the emergence of the lineage known as H58 (genotype 4.3.1) as a primary driver of an increasing number of typhoid fever cases. A recent modelling study using data generated in Blantyre, Malawi, identified multidrug resistant (MDR) S. However, there is a paucity of recent data on the frequency of carriers in different settings including sub-Saharan Africa (SSA) as well as the extent to which they contribute to disease transmission Gauld et al., 2018. In Africa, overall typhoid is now estimated to have an average annual pooled incidence rate of 112.1 (95% CI, 46.7–203.5) cases per 100,000 people Hopewell and Graham, 2014 Marchello et al., 2019 with a case fatality rate (CFR) of 5.4% (2.7–8.9) Marchello et al., 2020.Ĭontrol of typhoid is impeded by asymptomatic carriage, which historically was estimated to account for 2–5% of individuals infected Levine et al., 1982 Parry et al., 2002 Thanh Duy et al., 2020. Typhi) is estimated to involve ~21.7 million illnesses and 216,000 deaths annually Crump and Mintz, 2010 Mogasale et al., 2014, with most of these occurring in lower and middle-income countries. Typhoid fever, caused by Salmonella enterica serovar Typhi ( S. International Diarrheal Diseases Research Centre, Bangladesh.Department of International Health, John’s Hopkins University, United States.Department of Microbiology and Immunology, The University of Melbourne at The Peter Doherty Institute for Infection and Immunity, Australia.Department of Infectious Diseases, Central Clinical School, Monash University, Australia.
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