Emerg Infect DisEIDEmerging Infectious Diseases1080-60401080-6059Centers for Disease Control and Prevention14626224303306502-071610.3201/eid0910.020716Letters to the EditorAntimicrobial Drug-resistant Salmonella Typhimurium (Reply to Helms)DahlJan*Danish Bacon and Meat Council, Copenhagen, DenmarkAddress for correspondence: Jan Dahl, Danish Bacon and Meat Council, Axeltory 3, 1609 Copenhagen V, Denmark; fax: 4533145756; email: JD@danskeslagterier.dk10200391013501350Excess Mortality Associated with Antimicrobial Drug-Resistant SalmonellaTyphimuriumAntimicrobial Drug-resistant Salmonella Typhimurium (Reply to Dahl)
In Reply to Helms: In the article by Helms et al., Helms concludes that infections with Salmonella Typhimurium strains resistant to ampicillin, chloramphenicol, streptomycin, sulfonamide, and tetracycline (hereafter referred to as penta-resistant) were associated with higher death rates than infections with non–penta-resistant S. Typhimurium. Helms also concluded that infections with quinolone-resistant (nalidixine-resistant) S. Typhimurium were associated with higher death rates than quinolone-susceptible S. Typhimurium (1).
Table 2 in Helms’ article provides information that enables close scrutiny of this conclusion and comparison of the excess mortality associated with penta-resistant, quinolone-susceptible S. Typhimurium with the excess mortality of non–penta-resistant S. Typhimurium (1). In this letter, the Table is based on the original table. However, two additional comparisons have been added: the p values, which are not based on the data but are approximations based on the parameters in the table.
Two-year relative death rate of patients infected with <italic>Salmonella</italic> Typhimurium, by antimicrobial susceptibility pattern. Registry linkage study including 2,047 patients and a random matched sample of 20,456 people from the Danish general population
Resistant
Susceptiblea
Deaths/cases
RRb (95% CIc)
31/1,094
2.4 (1.6-3.7)
Deaths/cases
RR (95% CI)
p-valued
Resistant to >1 drug
13/393
3.5 (1.7-7.2)
28/953
2.3 (1.5-3.5)
0.86
Ampicillin
16/347
5.1 (2.6-10.2)
46/1,654
2.1 (1.5-3.0)
0.21
Chloramphenicol
13/458
2.1 (1.1-4.1)
43/1,700
1.9 (1.4-2.8)
0.01
Streptomycin
31/969
2.5 (1.6-3.9)
46/1,589
2.4 (1.7-3.4)
0.76
Sulfonamides
15/513
2.2 (1.2-4.1)
28/1,078
2.1 (1.4-3.3)
0.60
Tetracycline
3/108
44/1,534
2.4 (1.7-3.4)
0.85
Kanamycin
5/83
10.3(2.8-37.8)
23/1,018
3.9 (2.2-6.7)
Quinolone
12/283
4.8 (2.2-10.5)
54/1,964
2.1 (1.6-3.0)
0.02
R-type ACSSuT
5/40
13.1 (3.3-51.9)
47/1,764
2.1 (1.5-2.9)
0.06
R-type ACSSuTNx
5/40
13.1 (3.3-51.9)
7/243e
2.9 (1.1-7.9)
0.09
aSusceptible refers to strains susceptible to the given antimicrobial drugs or combination of antimicrobial drugs; first cell refers to pansusceptible strains. bDeath rate relative to the general population, as estimated by conditional proportional hazards regression analysis, controlling for underlying illness; RR=rate ratio. cCI=confidence interval. dp-value for test of homogeneity, i.e., RR for resistant being the same as for susceptible strains. eStrains with R-type ACSSuT, but quinolone sensitve.
The conclusion is that only quinolone resistance is associated with excess mortality compared with nonresistant isolates. Penta-resistant, quinolone-susceptible S. Typhimurium has a risk ratio of 2.9 (1.1 to 7.9) compared to the ratio of non–penta-resistant isolates 2.1 (1.5 to 2.9). When these figures are compared, the approximate p value is 0.55, which, of course, is far from being significant. Thus, on the basis of the article by Helms, penta resistance may not pose a greater threat to human health than non–penta resistance. However, the measured effect of penta resistance is achieved by the inclusion of quinolone-resistant S. Typhimurium in the group.
aRR, relative risk; CI, confidence interval. bAdjusted for coexisting conditions. cCompared to the non-penta group. dApproximations based on the parameters from the table.
Suggested citation for this article: Dahl J. Antimicrobial drug-resistant Salmonella Typhimurium (reply to Helms). Emerg Infect Dis [serial online] 2003 Oct [date cited]. Available from: URL: http://www.cdc.gov/ncidod/EID/vol9no10/02-0716.htm