Shigellosis, also called bacillary
dysentery, is caused by four species namely: Shigella dysenteriae, Shigella flexneri, Shigella boydii and Shigella
sonnei. Shigella was discovered over 100 years ago by the Japanese
microbiologist, Kiyosi Shiga for whom the genus is named.
Bacillary
dysentery is primarily a human disease often transmitted by the consumption of
food or drinking water contaminated with human faeces. Shigellosis can also be
transmitted sexually. Sexual transmission of Shigella was first described in
the United States during the 1970s. Since then, several outbreaks of sexually
transmitted Shigella, predominantly in Men who have Sex with Men (MSM),
have been reported. In 2006, an outbreak of Shigella among MSM in London
coincided with a similar outbreak in Berlin suggesting that travel plays a role
in introducing Shigella species to populations at risk.
Man is the only significant reservoir of Shigella infection.
Other
enteric illnesses, such as those caused by hepatitis A, Entamoeba histolytica, Giardia lamblia, Campylobacter, and Salmonella, also can be transmitted sexually.
Because faeces can contain multiple pathogens, polymicrobial infections can
result from a single sexual exposure. Outbreaks of sexually transmitted
shigellosis might be observed more frequently than outbreaks of other sexually
transmissible enteric organisms because the infectious dose is lower - as few
as 10 to 100 organisms can cause disease - the illness produces symptoms that
are more likely to bring patients to medical attention, and laboratory
diagnosis is simpler.
The incubation period is between 12 and 96
hours. Illness is characterized by diarrhea, sometimes with blood and mucus and
is common amongst young children although infection can occur in all ages after
travel to areas where hygiene is poor. Invasive disease is rare but extra
intestinal complications such as Haemolytic Uraemic Syndrome can occur. Cases
maintain a low level of infectivity for as long as the organism is excreted in
the stool. Shigella species may survive for up to 20 days in favorable
environmental conditions and this may lead to transmission through contact with
contaminated fomites.
In the Eurosurvelliance an article was
published on an ongoing investigation by the Health Protection Agency (HPA)
into the outbreak of Shigella flexneri serotype
3a in men who have sex with men in England and Wales using data from 2009 to
2011. An increase in UK-acquired cases of the infection was detected in London in
November 2010 and Greater Manchester during the spring of 2011 and as a result
a national outbreak control team (OCT) was established in September 2011 and an
enhanced surveillance was set up to collect additional information for all
laboratory-confirmed cases with sample dates between 1 September and 31
December 2011.
S. flexneri diagnoses
reported by the national laboratories between 2001 and 2011 were also analysed
to provide context to the current outbreak and to produce historical time
trends.
One
hundred and forty-five S. flexneri cases
were diagnosed during the enhanced surveillance period between September and
December 2011. Thirty-seven (25.5%) of these cases were non-travel related – a
non-travel related case was defined as a laboratory confirmed case of S. flexneri with a specimen date
between 1 September and 31 December 2011 with no recent travel.
Thirty-one of these cases were
confirmed as being UK-acquired whereas six reported diagnoses were likely to be
secondary cases linked to a symptomatic contact with recent travel to a
high-risk country.
Eighty-six
cases (59.3%) were associated with travel to high-risk countries - high-risk travel-associated
diagnoses was defined as individuals who returned to the UK in the four days
before onset of illness after travel to countries with high risk for Shigella
infection (South America, Asia and Africa) - and the travel history was
unknown for 22 individuals (15.2%). No low-risk travel-associated cases of S.
flexneri were reported during the enhanced surveillance period - low-risk
travel-associated individuals was defined as individuals who returned to the UK
in the four days before onset of illness after travel to countries with low
risk for Shigella infection (Europe, North America and Australia).
The
UK-acquired cases were mainly males (n=26) with eleven of these male cases
reporting MSM activity in the week before developing gastroenteritis. Interviews
with seven MSM cases showed that they all had one long term partner and
attended regular medical examinations. However, all cases reported having a
casual sexual partner in the week preceding illness. These interviews revealed
lack of awareness about Shigella and of the risks associated with
unprotected oral and oral-anal sex. Ten of the thirty-one reported UK-acquired S.
flexneri cases were serotype 3a.
From there investigations
it was discovered that the historical time trends in diagnosed cases of
shigellosis between 2001 and 2011 showed a gradual increase in the number of
cases in both males and females with no or unknown history of travel up until
2008. However, from 2009 onwards, the number of diagnosed male cases increased
rapidly compared to that of females.
Based on this study a
strong association was observed between UK-acquired S.flexneri and transmission in MSM despite the fact that some individuals
refused to disclose their sexual orientation. This outbreak will continued to
be monitored, in the mean time some control measures aimed at effective
management of cases and prevention of transmission have been put in place.
These include:
- Awareness
among clinicians and MSM
- Prompt
diagnosis and treatment
- Increased
testing of MSM with diarrhoea
- Treatment
of laboratory confirmed cases
As well as behavioural changes such
as:
- Wash
hands after use of toilets, before preparing or eating food and after sexual activity;
- Avoid
anal sex, oral-anal, scat and rimming whilst
symptomatic and until test for infection shows clearance;
- Use of condoms, gloves, dental dams during sex;
- Avoid sharing douching materials and sex toys;
- Avoid swimming pools and spa centres whilst ill and for two
weeks after recovery.
Work is
still ongoing by the investigators into identifying other risk factors for
infection and evaluating other possible control measures such as screening of
asymptomatic contacts.
