Typhoidal Salmonella and Emerging Resistance in Outbreak Proportions

Salmonella enterica subspecies enterica serotypes Typhi, Paratyphi A, Paratyphi B and Paratyphi C cause an acute, invasive and potentially fatal systemic infection known as typhoid fever or enteric fever. Among the 12 to 22 million patients of typhoid fever per annum, the estimated death rate is between 129 000 and 217 000, and 80% of these cases and deaths occur in Asia alone. Due to improved sanitation, most developed countries in Europe and North America are free from enteric fever, but enteric fever is still a disease of concern in Southeast Asia, the Indian subcontinent, Africa, and, to a lesser extent, in South America.1-3 Regions with the highest incidence of enteric fever are South-Central Asia and Southeast Asia. Salmonella has been responsible for numerous outbreaks in the Indian subcontinent, Southeast Asia, and Africa. In Delhi, India, the incidence rate is 9.8 cases/1000 person per year.4-6 Salmonella is a common cause of traveler’s diarrhea presenting with fever, nausea, vomiting, and abdominal cramps. Up to 70% of travelers from Western countries develop traveler’s diarrhea in the first week of travel to tropical destinations in South Asia and Southeast Asia. Highrisk regions for traveler’s diarrhea are Asia, the Middle East, Africa, Mexico, Central and South America. Intermediate-risk regions are Eastern Europe, South Africa, and some Caribbean islands. Low-risk regions are Northern and Western Europe, http://ijtmgh.com Int J Travel Med Glob Health. 2018 May;6(2):64-68 doi 10.15171/ijtmgh.2018.12 TMGH IInternational Journal of Travel Medicine and Global Health J

the United States, Canada, Australia, New Zealand, and Japan.[9][10] Effective antimicrobial therapy is required to control morbidity and mortality from typhoid fever.Until the 1960s, all Salmonella were susceptible to a wide range of antimicrobials.Ampicillin, chloramphenicol, and trimethoprimsulfamethoxazole were the first line drugs for Salmonella.Since 1962, plasmid-mediated resistance has appeared worldwide.Extensive epidemics caused by chloramphenicol resistant Salmonella Typhi were first witnessed in India and Mexico in 1972. 11,12By the late 1980s, multidrug-resistant Salmonella resistant to all first line drugs emerged worldwide including in India which is an endemic zone for 50%-80% of multidrug-resistant Salmonella.Since 1989, outbreaks by Salmonella Typhi resistant to chloramphenicol, ampicillin, trimethoprim, sulfonamides, streptomycin, and tetracyclines have been reported from India and Pakistan.][15][16] Ciprofloxacin became the antibacterial of choice for the treatment of typhoid fever after the emergence of Salmonella Typhi strains resistant to chloramphenicol.Ciprofloxacin is also recommended for traveler's diarrhea.However, the minimal inhibitory concentration (MIC) of ciprofloxacin against Salmonella Typhi is gradually increasing due to its continuous use.][19][20] Ceftriaxone is safe and efficacious against most clinical isolates of Salmonella and is now the preferred drug for MDRTF infections. 21,22Reports of resistance to cephalosporins have been appearing at an increasing rate since 2006.It is pertinent to monitor the resistance characteristics of multidrug-resistant Salmonella infections to enable empirical therapy and the treatment of complications.The spread of MDR and fluoroquinolone resistance in Salmonella presents increased clinical challenges in countries where enteric fever is imported, requiring enhanced surveillance.This study characterizes demographical trends, etiological and emerging resistance patterns in typhoidal Salmonella at a 1000-bed teaching hospital in New Delhi, India.

Methods
This prospective study was conducted among all patients determined to have typhoidal Salmonella infections from blood cultures in a 1000-bed tertiary-care hospital over a period of 6 months after approval was obtained from the Institutional Ethics Committee (ICMR STS 2017-01590).All 200 patients with Salmonella infections detected in blood cultures were included in the study.Typhoidal Salmonella isolated from samples other than blood, patients of nontyphoidal Salmonellosis, and repeat isolates were excluded.Blood samples were collected by skin puncture in Bact/Alert blood culture bottles (Biomerieux, France) following strict aseptic techniques.The quantity of blood drawn was 10 mL for adults and 5 mL for children.Samples were immediately transported to the microbiology laboratory for incubation in the Bact/Alert blood culture system (Biomerieux, France) for 2-120 hours.Subcultures on blood and McConkey agars were incubated for 24-48 hours at 37°C.Inpatients in pediatrics, obstetrics-gynecology, medicine, the intensive care unit (ICU), and OPD were under surveillance.Organism identification and antimicrobial susceptibility were accomplished using standard microbiology techniques and employing routine bacteriological methods, such as colony characteristics, gram staining, motility, carbon-source utilization, and enzymatic activity, and confirmed by the VITEK-2 Compact Automated Microbiology system (Biomerieux, France).Each patient's demographic profile and non-repeat positive cultures with respective antibiograms were taken into account in the profiling of isolates and antimicrobial susceptibility.Descriptive statistics including frequency, percentages, and 95% CIs were worked out using Microsoft Excel.

Discussion
Enteric fever is more common in tropical regions because of flooding of rain water, the distribution of sewage into drinking water sources, and increased bacterial concentrations in rivers and streams in the hot and dry season.The distribution of typhoid fever is not well documented in developing countries, because facilities capable of performing the blood culture tests essential for diagnosis are far and few, or because it remains unknown or unaffordable to many patients from resourcelimited communities.The incidence of typhoid fever may be as high as 1000 patients per 100 000 population per year in certain regions.In such regions, the excretion of Salmonella Typhi in feces is the main source of infection, and children are predominantly affected.Salmonella infections are associated with poverty; therefore, they tend to cause infections in families and communities. 23ravelers to tropical destinations are increasingly at risk of Salmonella infections when traveling to villages or remote rural areas of the countryside where diagnostic and treatment facilities may be far and few.Special precautions are required for travelers with pre-existing bowel/systemic problems such as irritable bowel syndrome, inflammatory bowel disease, poorly controlled diabetes, hepatic cirrhosis, or renal impairment.][26][27] The current study revealed a young patient profile suffering from Salmonella bacteremia.The high degree of resistance to fluoroquinolones is alarming among all serotypes, viz.Salmonella Typhi, Salmonella Paratyphi A, and Salmonella Paratyphi B. Almost all strains of Salmonella Paratyphi A were resistant to quinolones.Four isolates of multidrugresistant Salmonella showed an increasing trend toward the emergence of resistance in uncomplicated typhoid.The Salmonella serotypes found in this study were 71% Salmonella Typhi, 26% Salmonella Paratyphi A, and 3% Salmonella Paratyphi B, which was in accordance with a study in Indonesia that showed the predominance of Salmonella Typhi over Salmonella Paratyphi. 28In the current study, there appears to be an increasing susceptibility to first line drugs such as ampicillin, chloramphenicol, and trimethoprimsulfamethoxazole; i.e.Salmonella Typhi susceptibility to more than three was 99%.The antimicrobial resistance rates of Salmonella Typhi differ among different countries in the world.A study in Pakistan showed that resistance rates of Salmonella Typhi and Salmonella Paratyphi were 66.1% for ampicillin, 88.2% for fluoroquinolone, and 66.5% for trimethoprim-sulfamethoxazole. 29A study in Nepal showed resistance rates of Salmonella Typhi against ampicillin and Salmonella Paratyphi against ciprofloxacin were 1.8% and 3.9%, respectively, while there was no resistance against trimethoprim-sulfamethoxazole. 30Another study in China showed that resistance rates of Salmonella Typhi and Paratyphi were respectively 0.8% and 2.0% for ampicillin, 13.5% and 5.9% for ciprofloxacin, 5.4% and 1.4% for sulfamethoxazole, 5.4% and 0.8% for levofloxacin, 10% and 5.4% for ceftriaxone, and 0% for meropenem and imipenem.A study in Bangladesh showed resistance rates were 68.4% for ampicillin, 39.5% for ciprofloxacin, 57.9% for trimethoprim, and 68.4% for sulfamethoxazole.A study in Vietnam showed 80.4% for ampicillin, trimethoprim, and sulfamethoxazole, and 0% for ciprofloxacin, while in Indonesia they were 1.8% for ampicillin and trimethoprim, 0% for ciprofloxacin, and 3.6% for sulfamethoxazole. 31Studies from 2001 to 2003 in Indonesia showed that 2.5% of Salmonella Typhi was resistant to ampicillin, while there was no or very low resistance against trimethoprim-sulfamethoxazole, ceftriaxone, or ciprofloxacin 13 A hospital-based study from 2006 to 2010 in Indonesia also showed similar results; Salmonella Typhi showed no resistance against trimethoprim-sulfamethoxazole, ciprofloxacin, or meropenem, 1.9% against ampicillin, 0.9% against ceftriaxone, and 1.6% against cefotaxime. 32A study done in Indonesia on the DNA profiles of Salmonella Typhi showed clear differences according to regions, but all the Salmonella Typhi isolates showed similar phenotypes which were susceptible to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole. 33DR Salmonella is an emerging problem which has led to increased mortality, particularly in infants and children below five years of age and those who are malnourished. 34alidixic acid-resistant Salmonella Typhi (NARST) over and above MDR Salmonella reduces treatment options for enteric fever.Ciprofloxacin was the most effective prophylactic antimicrobial and the drug of choice for traveler's diarrhea until the emergence and high prevalence of resistance in Salmonella, Shigella, and Campylobacter.Improvements in public sanitation facilities, the rational use of antibacterials, clean drinking water, safe food handling practices, publichealth education, and mass immunization in endemic areas are required for the prevention of Salmonella infections.3][44] The overlapping epidemicity of Salmonella Typhi and Salmonella Paratyphi A emphasizes a bivalent vaccine covering both as an apparently better choice than a monovalent vaccine in the control strategy of enteric fever.

Conclusion
Typhoid remains an important public health problem in tropical developing countries threatening both residents and travelers.Salmonella Typhi remains the predominant serotype followed by Salmonella Paratyphi A. The high prevalence of quinolone resistance in Salmonella Typhi and Salmonella Paratyphi A is a serious problem limiting empirical therapy to non-quinolone-based therapy such as ceftriaxone.Multidrugresistant Salmonella is an emerging problem requiring active surveillance among residents and travelers presenting with tropical fever in hospitals, communities, and mass-gathering scenarios.

Figure 1 .
Figure 1.Clinicodemographic Profile of Patients Suffering From Typhoid Fever.

Table 1 .
Distribution of Salmonella Typhi, Salmonella Paratyphi A, and Salmonella Paratyphi B in Blood Samples From Various Wards

Table 2 .
Resistance patterns of Salmonella Typhi and Salmonella Paratyphi A and B