Molecular Epidemiology and Antibiotic Susceptibility of Vibrio cholerae Associated with a Large Cholera Outbreak in Ghana in 2014

Abstract

Background: Ghana is affected by regular cholera epidemics and an annual average of 3,066 cases since 2000. In 2014, Ghana experienced one of its largest cholera outbreaks within a decade with more than 20,000 notified infections. In order to attribute this rise in cases to a newly emerging strain or to multiple simultaneous outbreaks involving multi-clonal strains, outbreak isolates were characterized, subtyped and compared to previous epidemics in 2011 and 2012.

Methodology/principal findings: Serotypes, biotypes, antibiotic susceptibilities were determined for 92 Vibrio cholerae isolates collected in 2011, 2012 and 2014 from Southern Ghana. For a subgroup of 45 isolates pulsed-field gel electrophoresis, multilocus sequence typing and multilocus-variable tandem repeat analysis (MLVA) were performed. Eighty-nine isolates (97%) were identified as ctxB (classical type) positive V. cholerae O1 biotype El Tor and three (3%) isolates were cholera toxin negative non-O1/non-O139 V. cholerae. Among the selected isolates only sulfamethoxazole/trimethoprim resistance was detectable in 2011, while 95% of all 2014 isolates showed resistance towards sulfamethoxazole/trimethoprim, ampicillin and reduced susceptibility to ciprofloxacin. MLVA achieved the highest subtype discrimination, revealing 22 genotypes with one major outbreak cluster in each of the three outbreak years. Apart from those clusters genetically distant genotypes circulate during each annual epidemic.

Conclusions/significance: This analysis suggests different endemic reservoirs of V. cholerae in Ghana with distinct annual outbreak clusters accompanied by the occurrence of genetically distant genotypes. Preventive measures for cholera transmission should focus on aquatic reservoirs. Rapidly emerging multidrug resistance must be monitored closely.

Fig 1. Weekly notification of suspected cholera cases.

The Disease Surveillance Service of the Ghana Health Service reports 20,120 cholera cases according to the WHO case definition between May 2014 and December 2014 with a peak number of 2,853 cases in the 35^th calendar week (25–31 August).

Fig 2. Spatial and temporal location of suspected cholera cases (Mai 2014-December 2014; n = 20,120).

As notified to the Disease Surveillance Service of the Ghana Health Service according to the WHO case definition suspected cholera cases are plotted by district by 5-week period panels. The figure was produced with Arc GIS 10.0 (ESRI: ArcGis Desktop: Release 10.2011).

Fig 3. Pulse-field gel electrophoresis (PFGE) dendrogram for Vibrio cholerae isolates (n = 45).

The three clusters A, B and C (bold letters) are based on a similarity cut-off of 95% (Dotted line; Dice coefficient, represented by UPGMA, 1.0% optimization and 1.5% tolerance). The geographical location, year of disease onset, serogroup, serotype and multilocus variable-number tandem-repeat (VNTR) analysis (MLVA) results are given for each V. cholerae isolate. Regional three-letter codes: ASH, Ashanti region; CEN, Central region; GAR, Greater Accra region; VOL, Volta region. District three-letter codes: AAN, Asante Akim North; ACC, Accra; ADE, Adentan; AGW, Agona-Swedru; AWS, Awutu-Senya; ASA, Ashaiman; GAE, Ga East; GAS, Ga South; GAW, Ga West; GOE, Gomoa East; GOW, Gomoa West; HOH, Hohoe; HOV, Ho; KPK, Kpone-Katamanso; LEK, Ledzekuku-Krowor; TEM, Tema.

Fig 4. Minimum spanning tree of multilocus variable-number tandem-repeat (VNTR) analysis (MLVA) for Vibrio cholerae isolates (n = 45) by year of disease onset.

Clonal complexes (CC 1, CC 2, CC 3) were defined as isolates connected through a chain of single-locus variants. Grey figures indicate the number of different alleles. Three-digit codes present the laboratory isolate number.