Three Epidemics of Invasive Multidrug-Resistant Salmonella Bloodstream Infection in Blantyre, Malawi, 1998–2014

Background. The Malawi Liverpool Wellcome Trust Clinical Research Programme (MLW) has routinely collected specimens for blood culture from febrile patients, and cerebrospinal fluid from patients with suspected meningitis, presenting to Queen Elizabeth Central Hospital (QECH), Blantyre, Malawi, since 1998. Methods. We present bloodstream infection (BSI) and meningitis surveillance data from 1998 to 2014. Automated blood culture, manual speciation, serotyping, and antimicrobial susceptibility testing were performed at MLW. Population data for minimum-incidence estimates in urban Blantyre were drawn from published estimates. Results. Between 1998 and 2014, 167 028 blood cultures were taken from adult and pediatric medical patients presenting to QECH; Salmonella Typhi was isolated on 2054 occasions (1.2%) and nontyphoidal Salmonella (NTS) serovars were isolated 10 139 times (6.1%), of which 8017 (79.1%) were Salmonella Typhimurium and 1608 (15.8%) were Salmonella Enteritidis. There were 392 cases of NTS meningitis and 9 cases of Salmonella Typhi meningitis. There have been 3 epidemics of Salmonella BSI in Blantyre; Salmonella Enteritidis from 1999 to 2002, Salmonella Typhimurium from 2002 to 2008, and Salmonella Typhi, which began in 2011 and was ongoing in 2014. Multidrug resistance has emerged in all 3 serovars and is seen in the overwhelming majority of isolates, while resistance to third-generation cephalosporins and fluoroquinolones is currently uncommon but has been identified. Conclusions. Invasive Salmonella disease in Malawi is dynamic and not clearly attributable to a single risk factor, although all 3 epidemics were associated with multidrug resistance. To inform nonvaccine and vaccine interventions, reservoirs of disease and modes of transmission require further investigation.