Predominance of multidrug-resistant Salmonella Typhi genotype 4.3.1 with low-level ciprofloxacin resistance in Zanzibar

BACKGROUND

Typhoid fever is a common cause of febrile illness in low- and middle-income countries. While multidrug-resistant (MDR) Salmonella Typhi (S. Typhi) has spread globally, fluoroquinolone resistance has mainly affected Asia.

METHODS

Consecutively, 1038 blood cultures were obtained from patients of all age groups with fever and/or suspicion of serious systemic infection admitted at Mnazi Mmoja Hospital, Zanzibar in 2015-2016. S. Typhi were analyzed with antimicrobial susceptibility testing and with short read (61 strains) and long read (9 strains) whole genome sequencing, including three S. Typhi strains isolated in a pilot study 2012-2013.

RESULTS

Sixty-three S. Typhi isolates (98%) were MDR carrying blaTEM-1B, sul1 and sul2, dfrA7 and catA1 genes. Low-level ciprofloxacin resistance was detected in 69% (43/62), with a single gyrase mutation gyrA-D87G in 41 strains, and a single gyrA-S83F mutation in the non-MDR strain. All isolates were susceptible to ceftriaxone and azithromycin. All MDR isolates belonged to genotype 4.3.1 lineage I (4.3.1.1), with the antimicrobial resistance determinants located on a composite transposon integrated into the chromosome. Phylogenetically, the MDR subgroup with ciprofloxacin resistance clusters together with two external isolates.

CONCLUSIONS

We report a high rate of MDR and low-level ciprofloxacin resistant S. Typhi circulating in Zanzibar, belonging to genotype 4.3.1.1, which is widespread in Southeast Asia and African countries and associated with low-level ciprofloxacin resistance. Few therapeutic options are available for treatment of typhoid fever in the study setting. Surveillance of the prevalence, spread and antimicrobial susceptibility of S. Typhi can guide treatment and control efforts.

Malaria prevalence and performance of diagnostic tests among patients hospitalized with acute undifferentiated fever in Zanzibar

Background

Control efforts in Zanzibar reduced the burden of malaria substantially from 2000 to 2015, but re-emergence of falciparum malaria has been observed lately. This study evaluated the prevalence of malaria and performance of routine diagnostic tests among hospitalized fever patients in a 1.5 years period in 2015 and 2016.

Methods

From March 2015 to October 2016, paediatric and adult patients hospitalized with acute undifferentiated fever at Mnazi Mmoja Hospital, Zanzibar were included. The malaria prevalence, and performance of rapid diagnostic test (RDT) and microscopy, were assessed using polymerase chain reaction (PCR) as gold standard.

Results

The malaria prevalence was 9% (63/731). Children under 5 years old had lower malaria prevalence (5%, 14/260) than older children (15%, 20/131, p = 0.001) and persons aged 16 to 30 years (13%, 15/119, p = 0.02), but not different from persons over 30 years old (6%, 14/217, p = 0.7). All cases had Plasmodium falciparum infection, except for one case of Plasmodium ovale. Ten malaria patients had no history of visiting mainland Tanzania. The RDT had a sensitivity of 64% (36/56) and a specificity of 98% (561/575), and microscopy had a sensitivity of 50% (18/36) and  a specificity of 99% (251/254), compared to PCR. The malaria parasitaemia was lower in patients with false negative results on RDT (median 7 × 10³ copies/µL, interquartile range [IQR] 2 × 10³ – 8 × 10⁴, p = 0.002) and microscopy (median 9 × 10³ copies/µL, IQR 8 × 10² – 7 × 10⁴, p = 0.006) compared to those with true positive RDT (median 2 × 10⁵ copies/µL, IQR 3 × 10⁴ – 5 × 10⁵) and microscopy (median 2 × 10⁵ copies/µL, IQR 6 × 10⁴ – 5 × 10⁵).

Conclusions

The study emphasizes that malaria was a frequent cause of febrile illness in hospitalized patients in Zanzibar in the years 2015-2016, particularly among school age children and young adults. We found evidence of autochthonous malaria transmission in Zanzibar. Compared to PCR, both RDT and microscopy had low sensitivity, and false negative results were associated with low parasitaemia. While low parasitaemia identified only by PCR in a semi-immune individual could be coincidental and without clinical relevance, clinicians should be aware of the risk of false negative results on routine tests.

Monovalent Rotavirus Vaccine Effectiveness and Impact on Rotavirus Hospitalizations in Zanzibar, Tanzania: Data From the First 3 Years After Introduction

Background

Low-income settings challenge the level of protection provided by live attenuated oral rotavirus vaccines. Rotarix (RV1) was introduced in the United Republic of Tanzania in early 2013, with 2 doses given at the World Health Organization-recommended schedule of ages 6 and 10 weeks, along with oral poliovirus vaccine.

Methods

We performed active surveillance for rotavirus hospitalizations at the largest hospital in Zanzibar, Tanzania, from 2010 through 2015. Using a case-test-negative control design, we estimated the vaccine effectiveness (VE) of 2 RV1 doses in preventing rotavirus hospitalizations.

Results

Based on 204 rotavirus case patients and 601 test-negative controls aged 5-23 months, the VE of 2 RV1 doses against hospitalization for rotavirus diarrhea was 57% (95% confidence interval, 14%-78%). VE tended to increase against hospitalizations with higher severity, reaching 69% (95% confidence interval, 15%-88%) against the severity score for the top quarter of case patients. Compared with the prevaccine period, there were estimated reductions of 40%, 46%, and 69% in the number of rotavirus hospitalizations among infants in 2013, 2014, and 2015, respectively, and reductions of 36%, 26%, and 64%, respectively, among children aged <5 years.

Conclusions

With data encompassing 3 years before and 3 years after vaccine introduction, our results indicate that successful delivery of RV1 on the current World Health Organization schedule can provide substantial health benefits in a resource-limited setting.