What is the issue?
The investigation of this outbreak has found around two thirds of adult male cases are occurring among men who have sex with men, who have not travelled overseas. These findings indicate that sexual transmission is likely to be playing an important role in local spread. Shigella infection is possible after a very small infectious dose.
Around 100 cases of shigellosis are notified in Victoria each year. This means that in the first third of 2014, the average annual notification total has already been exceeded.
Analysis of Shigella isolates in this outbreak also confirms that there is resistance to a range of antibiotics recommended in the Therapeutic Guidelines for treatment of shigellosis. As a result, please seek advice from your diagnostic laboratory on the results of antibiotic susceptibility testing in each instance.
As in previous years, there continues to be a small number of cases related to overseas travel.
Symptoms and transmission
Transmission of Shigella is by the faecal-oral route, and the incubation period is usually 1-3 days.
Shigellosis is characterised by an acute onset of diarrhoea, fever, nausea, vomiting and abdominal cramps. Typically, stool contains blood, mucus and pus, although some persons will present with watery diarrhoea without these features.
Cases remain infectious as long as bacteria are shed in the faeces, which can be up to four weeks after symptoms resolve. Rarely, a carrier state may persist for months or longer. Appropriate antibiotic treatment usually reduces the duration of carriage to a few days and is recommended for public health reasons as a very low inoculum causes infection.
Stool culture is the best test for the diagnosis of shigellosis and will also provide confidence that the right antibiotic has been selected.
PCR is also available but does not provide information on antibiotic resistance. Also, PCR does not give biotype information which is needed to inform an understanding of the epidemiology of this outbreak, especially origins and links between cases.
Hand washing with soap and water is vital after any sexual contact, especially before preparing or eating food.
Appropriate antibiotic treatment usually reduces the duration of carriage to a few days and is recommended for public health reasons. Antimicrobial resistance is commonly found in Shigella isolates and has been observed in this outbreak against some antibiotics recommended in the Therapeutic Guidelines for treatment of shigellosis. Most isolates characterised in 2014 were sensitive to ciprofloxacin. The Department recommends that you seek advice from your diagnostic laboratory on the results of antibiotic susceptibility testing in each instance.
Food handlers, child care workers and health care workers should be excluded from work until two successive faecal specimens (collected 24 hours apart but not sooner than 48 hours following the discontinuance of antibiotics) are found to be free of Shigella.
Additionally, men who have sex with men are recommended to participate in 3-6 monthly sexual health testing if any of the following apply to them:
- there have been any episodes of unprotected anal sex
- there have been more than 10 partners in the past six months or
- the person has participated in group sex or used recreational drugs during sex.