Lathi Nair*, Sudarsana J*, Pushpa KK**

*Professors of Microbiology 
**Postgraduate in Microbiology
Department of Microbiology,Medical College Calicut


Address for correspondence 
Dr.Lathi Nair,
Professor of Microbiology,
Medical College, Calicut
Kerala, India
E-Mail: drlathi@rediffmail.com 



ABSTRACT 

Enteric fever is classically caused by Salmonella enterica serotype typhi, but serotypes paratyphi A and paratyphi B can also cause enteric fever, however the symptoms are milder and the mortality is lower. Salmonella paratyphi A was only occasionally isolated from cases of enteric fever in Calicut till 2001 (11.1%). But from 2002 there has been a sudden increase in enteric fever cases caused by S.paratyphi A (59%). The S.paratyphi A isolates till 2001 were all sensitive to Ampicillin, Cotrimoxazole, Furoxone, Chloramphenicol, Ciprofloxacin and Ceftriaxone but decreased susceptibility to Ciprofloxacin was observed by the Nalidixic acid screening test, in 2002 it was (78.6%) and in 2003 (100%). Multiple drug resistance in (MDR) S.paratyphi A was very low (1.7%).

Key words : S.Paratyphi A, Ciprofloxacin resistance



INTRODUCTION

Enteric fever is a major public health problem in India accounting for more than 300,000 cases per year and salmonella typhi is the commonest etiological agent(1). Earlier reports from India showed S.paratyphi A as the causative agent in 3% - 17% of enteric fever cases(2). A retrospective analysis of records at the All India Institute of Medical Science (AIIMS) New Delhi over a 5 year period (1994 - 98) showed that the proportion of S.paratyphi A in enteric fever cases rose from 6.5% in 1994 to 44.9% in 1998(3). Although outbreaks of MDR S.typhi and increase in the number of strains with decreased susceptibility to Ciprofloxacin have occurred, cases of drug resistant S.paratyphi A have been relatively uncommon in India(2). The typhoid salmonella isolates from 1999 to 2003 from this institution is given in table 1. Only one isolate of S.paratyphi A (3.6%) in the year 2002 was multidrug resistant to Ampicillin(A), Cotrimoxazole (Co) and Chloramphenicol (C)and in 2003 one isolate (4.3%) was resistant to Ampicillin (A) & Cotrimoxazole (Co) as shown in Table 2. Nalidixic acid screening done on the 57 isolates of S.paratyphi.A (from 2000 - 2003) showed Nalidixic acid resistance in 45 isolates (78.9%) showing patients' unresponsiveness to Ciprofloxacin in the usual therapeutic dose. (Table -2 ).




MATERIALS & METHODS

A retrospective study of the typhoid salmonella isolates from 1999 - 2003 was done. The strains were tested for susceptibility to Ampicillin (10mg), Chloramphenicol (30mg), Trimethoprim/ Sulfamethoxazole (1.25/23.75mg), Furoxone (100mcg), Ciprofloxacin (5mg), Ceftriaxone (30mg) and Nalidixic acid (30mg) by the KIRBY BAUER disc diffusion method. Nalidixic acid screening test for typhoid salmonella isolates is done routinely in the laboratory from 1999 onwards. Clinical features of 20 patients from whom S.paratyphi A was isolated in 2002 was studied in detail. 




RESULTS 

The sensitivity pattern of S.paratyphi A isolates is shown in Table 2 and percentage of MDR typhoid salmonella is shown in Table 3. Out of the 57 S.paratyphi A isolates, one strain was multidrug resistant to A, Co & C and another strain to A & Co. The rest of the 55 isolates were sensitive to all drugs as shown in Table 2. Of the 57 isolates subjected to Nalidixic acid screening test (2000 - 2003), 45 isolates (78.9%) were Nalidixic acid resistant (Table 2). Clinical features of the 20 patients are shown in Table 4. All patients presented with fever, of which 13 patients (65%) had high-grade fever with chills and rigor and 7 patients (35%) had low-grade fever. Headache was seen in 13 patients (65%), diarrhoea in 10 patients (50%), 5 patients (25%) had hepatosplenomegaly and one patient (5%) had meningism. Widal test was done for 8 of these patients of which 5 of them had S.para A H antibody titre > 1/100.
S.typhi 0 > 1/100 & S.typhi H < 1/100. For the other 3 patients Widal test was negative. The antibiotics given for treating these patients were Ciprofloxacin, Ceftriaxone and Chlormaphenicol. 1 patient recovered without taking any antibiotic. All patients got cured with a mean hospital stay of 8 days.





DISCUSSION 

Enteric fever is endemic in all parts India. Enteric fever caused by drug resistant S.typhi has been reported earlier from this institution(4,5). From 2002 there has been a substantial decrease in the incidence of MDR S.typhi in Calicut(6). S.paratyphi A has been less frequently isolated from cases of enteric fever in Calicut till 2001. In 2001 the percentage of S.paratyphi A isolates was 11.1% but it abruptly increased to 59.6% in 2002 and 59% in 2003. With the exception of two S.paratyphi A isolates all the rest were sensitive to Ampicillin, Cotrimoxazole, Chloramphenicol, Furoxone, Ciprofloxacin and Ceftriazone. 45 strains (78.9%) were Nalidixic acid resistant, there by indicating treatment failure with Ciprofloxacin in the usual therapeutic dose. The incidence of enteric fever caused by drug resistant. S. paratyphi A abruptly increased in New Delhi to 24% in 1998 and most drug resistant isolates in 1999 showed higher MIC to Ciprofloxacin.(7) In India the estimated ratio of S.typhi to S.paratyphi A is 10:1(8) but in Calicut from 2002 the ratio is 1:1.5. A study of the molecular typing on the sudden emergence of S.paratyphi A enteric fever in New Delhi in 1996 by IS 200 probing and plasmid profiling suggested that genetic rearrangements could occur during outbreaks(9). So also the wide spread use of vaccines and Quinolones against S.typhi in the past decade may have been responsible for the sudden increase in incidence of enteric fever caused by S.paratyphi A. Multi drug resistant S.typhi was endemic in Calicut from 1989 (68.7%) but since 2002 the incidence of MDR S.typhi has decreased substantially (21.05%)(6). However multiple drug resistance has not been a problem for S.paratyphi A so far in our institution (Table 3). But low-level resistance to Ciprofloxacin was seen as shown by the Nalidixic acid screening test, so these patients will not respond to Ciprofloxacin in the usual therapeutic dose. The high incidence of S.paratyphi A found in the present study indicates the emergence of this uncommon pathogen as a major cause of enteric fever in Calicut. 

REFERENCES 

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