Human salmonella isolates 2021

The number of Salmonella isolates confirmed this year (n=668) showed a decrease in comparison with 2020 (n= 726). This decrease is most likely due to a reduction of imported cases as a result of NZ's closed border COVID-19 containment strategy.

Salmonella Typhimurium ST19 was the predominant type, representing 22.3% of total isolates. 5-SNP clustering of all cases showed this to be a diverse group.

The main Salmonella serotype showing an increase this year in comparison with 2020 was S. Enteritidis (from 9.9% to 19.3%). This was due to two separate events:

• A cluster of 28 cases of Salmonella Enteritidis ST183, locally designated 5-SNP cluster type _2021_C_01, which was detected in January and February 2021 and predominantly dispersed within the South Island. A common food source was not confirmed.
• Forty-nine cases adding to the Salmonella Enteritidis ST11 locally designated 5-SNP cluster type _2019_C_01. The cases were geographically dispersed and a source for the outbreak was confirmed as being from the poultry industry.

Salmonella serotype showing a decrease this year in comparison with 2020 included: S. Typhi (from 3.6% to 0.4%). This can be wholly attributed to closed borders.

The number of isolates (n=85) confirmed this month showed a decrease in comparison to the number of isolates confirmed in January 2020 (n=136). Salmonella Typhimurium ST19 (25% in 2020 vs 22.4% in 2020) were the most common serotypes confirmed this month. Uncommon serotype confirmed this month was Salmonella Kedougou (13 human cases since it was first confirmed in New Zealand in 1996)

The number of isolates (n=78) confirmed this month showed a decrease in comparison to the number of isolates confirmed in February 2020 (n=91). Salmonella Enteritidis ST183 (42.3% in February 2021 vs 5.5% in February 2020) was the most common type confirmed this month. Cases were predominantly in the South Island.

The number of isolates (n=78) confirmed this month showed an increase in comparison to the number of isolates confirmed in March 2020 (n=94). Salmonella Typhimurium ST19 (18% in March 2020 vs 23% in March 2021) was the most common serotypes confirmed this month.

The number of isolates (n=79) confirmed this month showed an increase in comparison to the number of isolates confirmed in April 2020 (n=26 low due to COVID-19 level 4 restrictions  ). Salmonella Typhimurium ST19 (34.6% in April 2020 vs 31.6% in April 2021) was the most common type confirmed this month. Uncommon serotype confirmed this month was Salmonella Mana (5 human cases since it was first confirmed in New Zealand in 1996)

The number of isolates (n=50) confirmed this month showed an increase in comparison to the number of isolates confirmed in May 2020 (n=40). S. Typhimurium ST19 (27.5% in May 2020 vs. 26% in May 2021) was the most common serotype confirmed this month. Uncommon serotype confirmed this month was Salmonella Waycross (13 human cases since it was first confirmed in New Zealand in 1996)

The number of isolates (n=57) confirmed this month showed a slight increase in comparison to the number of isolates confirmed in June 2020 (n=33). Salmonella Typhimurium ST19 (18.2% in June 2020 vs 24.6% in June 2021) was the most common serotype confirmed this month.

The number of isolates (n=42) confirmed this month showed a slight increase in comparison to the number of isolates confirmed in July 2020 (n=39). Salmonella Typhimurium ST568 (28.2% in July 2020 vs. 26.2% in July 2021) was the most common serotype confirmed this month.

The number of isolates (n=34) confirmed this month showed an increase in comparison to the number of isolates confirmed in August 2020 (n=53). Salmonella Typhimurium ST19 (20.8% in August 2020 vs 35.3% in August 2021) was the most common serotype confirmed this month.

The number of isolates (n=40) confirmed this month showed a decrease in comparison to the number of isolates confirmed in September 2020 (n=63). Salmonella Typhimurium ST19 (14.3% in September 2020 vs. 27.5% in September 2021) was the most common serotype confirmed this month. Uncommon serotypes confirmed this month were Salmonella Orion (14 human cases since it was first confirmed in New Zealand in 1993) and Salmonella Uganda (21 human cases since it was first confirmed in New Zealand in 1994).

The number of isolates (n=46) confirmed this month showed a decrease in comparison to the number of isolates confirmed in November 2020 (n=52). Salmonella Typhimurium ST568 (9.6% in November 2020 vs. 26.1% in November 2021) was the most common serotype confirmed this month. Uncommon Salmonella serotype confirmed this month was S. Orion (14 human isolates since it was first confirmed in New Zealand in 1993).

The number of isolates (n=46) confirmed this month showed a decrease in comparison to the number of isolates confirmed in November 2020 (n=52). Salmonella Typhimurium ST568 (9.6% in November 2020 vs. 26.1% in November 2021) was the most common serotype confirmed this month. Uncommon Salmonella serotype confirmed this month was S. Orion (14 human isolates since it was first confirmed in New Zealand in 1993).

The number of isolates (n=42) confirmed this month showed no change in comparison to the number of isolates confirmed in December 2020 (n=42). Salmonella Typhimurium ST19 (28.6% in December 2020 vs 31% in December 2021) was the most common serotypes confirmed this month. Uncommon Salmonella serotypes confirmed this month were S. Bardo (12 human isolates since it was first confirmed in New Zealand in 1989) and S. Kedougou (14 human isolates since it was first confirmed in New Zealand in 1996).