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Correction to COVID-19 case rates data

Between 10 April and 27 April, published rolling-average case rates for COVID-19 were incorrect due to an error in population estimates used to calculate these metrics. As of 4pm on 28 April, these have been corrected. More information.

BackEntry title:

Monthly rate per 100,000 population of invasive Group A Streptococcus (iGAS) cases

Last updated on Thursday, 10 April 2025 at 03:31pm

Summary

Topic
iGAS
Category
cases
API name
iGAS_cases_rateByMonth

Rationale

To highlight the most recent monthly regional activity in invasive Group A Streptococcus (iGAS) cases.

Definition

This metric shows the monthly rate per 100,000 of reported iGAS episodes. New iGAS episodes are reported by specimen date – the date the first sample that identified the infection was taken from an individual.

Only isolates with an invasive specimen type are included, these are specimens taken from a normally sterile site.

Region is derived from the patient postcode supplied with the laboratory specimen, and where not available the laboratory postcode is used.

Age group and sex are derived from the information supplied with the laboratory specimen.

Methodology

Cases of iGAS are formally diagnosed from positive microbiological diagnostic test results (culture or molecular) identifying group A streptococcus from a sample taken from a normally sterile site. As invasive GAS is a notifiable infection, all positive samples will be reported to the UKHSA Second Generation Surveillance System (SGSS). This metric displays these positive samples.

SGSS is an application that stores and manages data on laboratory isolates and notifications collected through surveillance. It is the preferred method for capturing routine laboratory surveillance data on infectious diseases and antimicrobial resistance from diagnostic laboratories across England.

Positive tests that belong to the same individual are grouped together and considered one episode, or result, if they are within 14 days of each other. Positive tests results that are 14 days apart (regardless of negative tests in between) are considered as a separate episode of infection.

Group A streptococcus (GAS) infections exhibit seasonal trends. A GAS season begins from International Standards Organisation (ISO) week 37 in one year to ISO week 36 in the following year (mid-September to mid-September).

Data is presented as a rate per 100,000, consisting of a sum of total cases in a month with the Office for National Statistics (ONS) mid-year population estimates as the denominator. Monthly rates are available by UKHSA Region, sex and age band.

Caveats

Where age or sex information is missing for an individual, these are not included in the monthly rate.

Data included is for England only.

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