Aura 2016: first Australian report on antimicrobial use and resistance in human health

4.9 Salmonella species

Health impact

Salmonella species are important causes of bacterial gastroenteritis. Most cases arise through foodborne transmission. Occasionally, gastroenteritis is complicated by septicaemia, although this is usually self-limiting. Two serotypes, Salmonella Typhi and Salmonella Paratyphi (together called ‘typhoidal Salmonella’), cause a distinct syndrome called enteric fever, where the organism is always invasive (causing septicaemia), and causes significant morbidity and mortality if untreated. Salmonella gastroenteritis is endemic in Australia, but almost all cases of enteric fever are seen in returned overseas travellers.

Treatment

Salmonella gastroenteritis is self-limiting. Antimicrobial therapy is generally contraindicated because it does not affect the course of the disease and will prolong intestinal carriage of the organism after disease resolution, increasing the risk of transmission. Antimicrobial therapy is indicated in patients with severe disease or septicaemia, and patients who have prosthetic vascular grafts. Ciprofloxacin, azithromycin and ceftriaxone are the standard treatments. These are also the agents of choice for patients with enteric fever.

Types and impact of resistance

Resistance to older treatment agents, such as ampicillin and chloramphenicol, has been seen for many years, but, so far, resistance to the newer agents has only been a problem with ciprofloxacin and other fluoroquinolones, such as norfloxacin. This has resulted in recent reassessment of the definition of fluoroquinolone resistance. Not all susceptibility testing systems are yet capable of applying the new definitions.

Key findings (national)

In nontyphoidal Salmonella species, rates of resistance were low for ampicillin, and very low for ceftriaxone and the fluoroquinolones (Figure 4.26). In contrast, rates of resistance in typhoidal Salmonella species to the fluoroquinolone ciprofloxacin were above 10% for blood isolates (Figure 4.27).

In nontyphoidal Salmonella species, rates of resistance were low for ampicillin, and very low for ceftriaxone and the fluoroquinolones. In contrast, rates of resistance in typhoidal Salmonella species to the fluoroquinolone ciprofloxacin were above 10% for blood isolates.

Figure 4.26 Nontyphoidal Salmonella species resistance, by specimen source, 2014

na = not available (either not tested or tested against an inadequate number of isolates)

Sources: OrgTRx (Queensland); Australian Group on Antimicrobial Resistance (national); Sullivan Nicolaides Pathology (Queensland and northern New South Wales)

Data table: Figure 4.26

Agent	Blood (n = 182), % resistant	Faeces (n = 2,426), % resistant	Other (n = 115), % resistant
Ampicillin	6.7	7.7	7.0
Ceftriaxone	0.6	0.8	1.9
Ciprofloxacin	1.1	0.2	0.0
Norfloxacin	na	1.4	0.9

Figure 4.27 Typhoidal Salmonella species resistance (blood culture isolates), 2014

Sources: OrgTRx (Queensland); Australian Group on Antimicrobial Resistance (national); Sullivan Nicolaides Pathology (Queensland and northern New South Wales)

Data table: Figure 4.27

Agent	Blood (n = 44), % resistant
Ampicillin	2.3
Ceftriaxone	0.0
Ciprofloxacin	12.2

Additional findings from targeted surveillance on blood culture isolates

Additional data on 30-day all-cause mortality for strains causing septicaemia and enteric fever is available from AGAR. There was no mortality at 30 days for typhoidal strains, and a modest mortality for nontyphoidal strains (Table 4.13).

Table 4.13 Onset setting and 30-day all-cause mortality for infections with Salmonella species (blood culture isolates), 2014

Species	Community, n	Community mortality, % (n)	Hospital, n	Hospital mortality, % (n)	Total, n	Total mortality, % (n)
Salmonella species (nontyphoidal)	66	7.6 (5)	2	0.0 (0)	68	7.4 (5)
Salmonella species (typhoidal)	22	0.0 (0)	0	0.0 (0)	22	0.0 (0)
Total	88	5.7 (5)	2	0.0 (0)	90	5.6 (5)

Source: Australian Group on Antimicrobial Resistance (national)