Friday, August 6, 2010


A ProMED-mail post

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International Society for Infectious Diseases

Date: Mon 2 Aug 2010
Source: CDC, Salmonella Outbreak Investigations [edited]

CDC is collaborating with public health officials in many states and
the FDA to investigate a multistate outbreak of Salmonella infection,
serotype I 4,[5],12:i:-. Investigators are using DNA analysis of
_Salmonella_ bacteria obtained through diagnostic testing to identify
cases of illness that may be part of this outbreak.

As of 9 pm EDT on 29 Jul 2010, a total of 34 individuals infected
with a matching strain of _Salmonella_ serotype I 4,[5],12:i:- have
been reported from 17 states since 1 Jan 2010. The number of ill
persons identified in each state with this strain is as follows: AL
(1), AZ (1), CO (1), GA (7), IA (1), IL (3), MA (3), MI (1), MO (3),
NC (3), NV (1), NY (2), SC (1), TN (1), VA (1), WI (3), and WY (1).

Among the persons with reported illness onset dates available,
illnesses began between 4 Dec 2009, and 9 Jun 2010. Infected
individuals range in age from less than 1 to 57 years old and the
median age is 12 years. 53 percent of patients are male. Among the 17
patients with available information, 1 (6 percent) was hospitalized.
As of 29 Jul 2010, no deaths attributed to this infection have been reported.

CDC and public health officials in multiple states are conducting an
epidemiologic study. Preliminary analysis of this study has suggested
an association with frozen rodents used for reptile feed. Ill persons
(61 percent) were significantly more likely than well persons (0
percent) to report any exposure to rodents in the week before
illness. Additionally, ill persons (26 percent) were significantly
more likely than well persons (0 percent) to report using frozen
rodents for reptile feed in the week before illness. An environmental
investigation was conducted by the FDA, and culture of samples
collected yielded Salmonella that matched the human outbreak strain.

Although referred to differently in the USA and UK, the strain in the
USA investigation is indistinguishable from the strain that caused an
outbreak in the United Kingdom in 2009. The outbreak investigation by
the Health Protection Agency of the UK implicated frozen mice
imported from the USA as food for pet reptiles as the source of human illness.

Communicated by:

[As noted in the CDC report the _S. enterica_ isolates I 4,[5],12:i:-
and DT191A are identical.

As a review, discussed by Ana Paccagnella (supervisor of the Enteric
Bacteriology Section at the British Columbia Centre for Disease Control),

_Salmonella_ as a genus has 2 species, _enterica_ and _bongori_. _S.
enterica_ is divided into 6 subspecies: _enterica_, _salamae_,
_arizonae_, _diarizonae_, _houtenae_, and _indica_. _S. enterica_
subspecies _enterica_ (or subspecies I) strains are the ones usually
isolated from humans or warm-blooded animals and represent a majority
of the salmonellas that are clinically important.

The designation _Salmonella_ I 4,[5],12:i:- means:
- the "I" reflects subspecies _enterica_;
- the "4, [5], 12" are the O (or somatic) antigens associated with
the organism; It should be noted that serotype Typhimurium carries
somatic antigens 4, 5 and 12 (the Group B antigens). Paccagnella
pointed out to me in an e-mail that an O antigen underscored or
placed in [ ] can refer to whether the antigen is related to phage
conversion or not.
- the nomenclature after the colon, in this case i:-, reflects the
flagellar or H antigens. It is these H antigens that define the
serotype identity within an individual group of salmonellas.

Almost all of these organisms are biphasic in regard to the H
antigens, that is, they can switch from 1 flagellar antigen to
another. As an example, _S._ Typhimurium is I 4, 5, 12:i:1,2. The
outbreak organism here, however, is monophasic. This monophasic
strain appears to be such due to the absence of the _flj_B gene which
is involved in the H antigen switching mechanism.

According to Paccagnella, around 1903 Smith and Reagh reported on the
different behavior of the flagellar and somatic antigens of
salmonella strains. Their work was mostly ignored until Weil and
Felix, working on _Proteus_ cultures, noted 2 forms, the swarming
form called the H form (_mit Hauch_, in English: with breath] and the
non-swarming form, called the O form (_ohne Hauch_, in English:
without breath). The H form contained both O and H antigens
(correctly termed the OH form). These parallels were transposed to
the salmonella antigens.

If O antiserum is added to a culture, motility is preserved whereas
if H antiserum is added the culture does not move. Therefore, H
antigen was involved with swarming in the agar plate (breathing might
have been used to imply the ability to move). (Salmonellas, of
course, do not swarm on certain agar plates like _Proteus_ do.) - Mod.LL]

[see also:
Salmonellosis, reptile feed - UK, USA: st Typhimurium DT 191A 20100730.2555
Salmonellosis, reptile feed - USA: recall 20100729.2545
Salmonellosis, serotype 4,[5],12:i:- - EU 20100606.1888]

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