Friday, April 13, 2018

UK: `Exceptional' Scarlet Fever Season Continues


For the past several months (see here and here) we've been checking in on the UK's mounting Scarlet Fever epidemic, which has eclipsed - by good measure  - anything seen in that country since the early 1980s.
While the reasons remain unclear (see The Lancet's Nov 2017 report  Resurgence of scarlet fever in England, 2014–16: a population-based surveillance study), Scarlet Fever has been on the ascendant since 2009 across much of Asia, and more recently in the UK.
Scarlet fever (Group A Streptococcus or GAS) is caused by the bacterium Streptococcus pyogenes - which like viruses, can evolve over time – sometimes resulting in increased virulence, greater transmissibility, and/or antibiotic resistance. 
Strains are identified by changes in their M-protein gene sequence (emm types) – which often determines virulence - and within these types new variants can emerge. 
Scarlet Fever primarily affects children under the age of 12, although adults can be affected. It is highly contagious, and while there is no vaccine, antibiotics are generally effective when treated early.

Far less common, albeit considerably more serious, is a related illness called iGAS (invasive Group A Strep), which indicates infection of the bloodstream, deep tissues, or lungs, and may result in severe (and frequently fatal) cases of necrotizing fasciitis and streptococcal toxic shock syndrome.

While children may be affected, iGAS most commonly occurs in older adults. As the chart below indicates, iGAS cases are running well above average as well. 

While their are hopeful signs this year's epidemic season may be starting to wane, the UK's PHE continues to urge vigilance in spotting signs of Scarlet Fever. Additional details are available in the following PHE report. 

Health Protection Report Volume 12 Number 13
Group A streptococcal infections: third report on seasonal activity in England, 2017/18

Surveillance of scarlet fever in England indicates a decline in notifications in recent weeks, however reported cases remain higher than the same period in the last four seasons (weeks 37 to 14, 2013/14 to 2016/17), a pattern reflected within the weekly GP consultation data [1,2]. This may indicate that we have passed the peak of the scarlet fever season but could in part reflect a delay in primary care access or reporting over the Easter bank holidays.
GPs, microbiologists and local authorities are asked to remain alert, and are reminded of the actions to be taken for every case, including: prompt notification to local Public Health England (PHE) Health Protection Teams (HPTs); obtaining throat swabs (prior to commencing antibiotics) when there is uncertainty about a diagnosis or when a case is part of an outbreak; and reinforcing the need for excluding cases or possible cases from school/work until antibiotic treatment has been commenced for a period of 24 hours [3].
The number of laboratory notifications of invasive group A streptococcal (iGAS) disease indicate continued elevation compared to recent seasons with possible early signs of decline. Frontline clinicians and microbiologists should be mindful of increases in invasive disease as the season progresses and maintain a high index of suspicion in  relevant patients, as early recognition and prompt initiation of specific and supportive therapy for patients with iGAS infection can be life-saving.
Rates of scarlet fever notification remain elevated but with early indications of a downturn in seasonal activity, as expected at this time of year. Weekly numbers of scarlet fever notifications this season have been higher than any previously recorded (weeks 11-13; weekly records available since 1982). Considered alongside the high numbers of GP consultations reported this season, this suggests genuinely exceptional levels of scarlet fevers [3].

While rates of scarlet fever remain high, close monitoring, rapid and decisive response to potential outbreaks and early treatment of scarlet fever is vital, especially given the potential complications associated with GAS infections.

The number of cases of iGAS disease notified through routine laboratory surveillance in England during 2018 is of concern, with weekly reports approaching 100 during February and March. Whether this increase is related to the heightened scarlet fever activity, or influenza activity, a known predisposing factor, is unknown.
Clinicians, microbiologists and HPTs should continue to be mindful of potential increases in invasive disease and maintain a high index of suspicion in relevant patients as early recognition and prompt initiation of specific and supportive therapy for patients with iGAS infection can be life-
        (Continue . . . )

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