Human Salmonella isolates, 2019 No.01, January

The number of isolates (n=179) confirmed this month showed an increase in comparison to the number of isolates confirmed in January 2018 (n=132). Salmonella Typhimurium 108/170 (0.0% in January 2018 vs 36.9% in January 2019) were the most common serotypes confirmed this month. Uncommon serotypes confirmed this month included Salmonella Brancaster (7 human cases since it was first confirmed in New Zealand in 2006) and Salmonella Enteritidis phage type 14c (2 human cases since it was first confirmed in New Zealand in 2018).

A national investigation into a cluster of Salmonella Typhimurium phage type 108/170 cases (Source: EpiSurv 1115 hours 12 February 2019, REDCap 1100 hours 12 February 2019, ESR Enteric Reference Laboratory)
• Since 01 January 2019 there have been 67 confirmed and 2 probable cases of Salmonella Typhimurium phage type 108/170 reported. This is a significant increase compared to the same period for previous years: 2018: 0, 2017: 2, 2016: 5, 2015: 1, 2014: 1. There were 4 cases of this phage type identified in 2018, 13 in 2017 and 19 in 2016.
• Multiple-Locus Variable number tandem repeat Analysis (MLVA) results are available for 64 cases. Of these, 60 have a common profile (European designation 3-6-9-NA-0311 and Australian designation 4-8-10-0-517) and one has a closely related profile (European designation 3-7-9-NA-0311 and Australian designation 4-9-10-0-517). Three cases have a profile sufficiently different from the outbreak profile and have been excluded from the cluster investigation for now. MLVA results are pending for 3 cases.
• ESR has recommended that all cases in this cluster (retrospectively and prospectively) are interviewed using a national hypothesis generating questionnaire administered in REDCap. This questionnaire has been used previously for outbreak investigations in NZ. The following case definition applies: Any person with symptoms of gastroenteritis notified in New Zealand with Salmonella Typhimurium phage type 108/170 (unless already found to have a MLVA type distinct from the cluster profile) since 23 December 2018. As of 1100 hours 12 February 2019, 38 questionnaires have been sufficiently completed and analysis of these is currently underway.
• The 64 confirmed cases meeting the current outbreak case definition were reported to the following DHBs: Waitemata (12), Counties Manukau (7), MidCentral (6), Capital & Coast and Hutt Valley (5 each), Waikato and Wairarapa (4 each), Northland, Auckland, Hawke's Bay, and Southern (3 each), Lakes, Tairawhiti and Taranaki (2 each), Bay of Plenty, Lakes, Whanganui, Nelson Marlborough and Canterbury (1 each). The 2 probable cases are household contacts of confirmed cases reported to Waikato and Lakes DHBs (1 each).
• Onset dates have been recorded for 58 cases and range from 23 December 2018 to 25 January 2019 (see epidemic curve attached). The epidemic curve and common MLVA profile is suggestive of a common source outbreak.
• Cases range in age from 2 to 92 years with the majority being adults 23 years or older (82.8%, 53/64 cases) with a median age of 38 years. 41 cases (64.1%) are female.
• Ethnicity was recorded for all 64 cases and distributed as follows: European/Other (47), Māori (11), Pacific Peoples (4) and Asian (2).
• 16 cases (25.0% 16/64) have been hospitalised. No cases have died.
• Note cases occurring in the Waikato/Lakes/Bay of Plenty region may not be identified, as Salmonella isolates have not been referred to ESR from Pathlab for serotyping since 5th November. Pathlab started sending Salmonella isolates from 21 January and 3 confirmed cases have since been identified via Pathlab, one each in in Bay of Plenty, Lakes and Waikato DHBs.