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Listeriosis in Portugal: an existing but under reported infection

  • Gonçalo N Almeida1,
  • Paul A Gibbs1,
  • Tim A Hogg1 and
  • Paula C Teixeira1Email author
Contributed equally
BMC Infectious Diseases20066:153

https://doi.org/10.1186/1471-2334-6-153

Received: 30 May 2006

Accepted: 20 October 2006

Published: 20 October 2006

Abstract

Background

Listeriosis is a rare disease caused by the bacterium Listeria monocytogenes, the normal vehicle of which is food. The disease, which is largely confined to its risk groups of pregnant women, the elderly and immunocompromised individuals, has increased in incidence in recent years.

In Portugal, listeriosis is not a notifiable infection and available data are scarce.

The objective of this work was to collate the available information concerning listeriosis in Portugal by compiling a retrospective study of cases recorded over a decade.

Methods

Requests for case data on clinically confirmed listeriosis, recorded over the previous decade, were replied to by 23 hospitals and a National Institute of Health delegation.

Results

35 cases of listeriosis were identified for the period between 1994 and 2003 inclusive, the mortality rate being greater than 17%. According to the data collected in this study for the year 2003, the incidence of this disease in Portugal was at least 1.4 cases per million inhabitants in that year.

Conclusion

The study demonstrates, for the first time in the widely available literature, that despite their being no cases of listeriosis in Portugal recorded in official reports, the threat of L. monocytogenes to public health is of a similar dimension to that in other countries.

Background

Listeria monocytogenes is an ubiquitous bacterium responsible for cases and outbreaks of listeriosis in humans and animals, normally transmitted by consumption of contaminated foods or feeds [1]. In recent years several outbreaks of listeriosis have been described, associated with the consumption of a wide variety of foods, ranging from dairy products, to ready-to-eat deli meats [1].

Although exposure to the bacterium is common [2], listeriosis is rare within the general population; incidence in Europe varies between 0.3 and 7.5 cases per million inhabitants with a mortality rate between 20 and 30% [3]. Certain groups within the general population are particularly susceptible to infection, namely immunocompromised persons, (e.g. organ transplant or cancer patients), HIV-infected individuals, pregnant women, newborn babies and the elderly [1]. In Portugal, listeriosis is not a notifiable infection and available data are scarce [4]. In a recent published document [3], it is stated "... all participating countries except Portugal have at least one surveillance system for listeriosis". Moreover, in a publication of the Portuguese National Health Services concerning advice for the prevention of infectious diseases during pregnancy [5], L. monocytogenes is not mentioned.

The present study aimed to contribute to the knowledge of listeriosis in Portugal through compiling a retrospective study of the cases identified over the period between 1994 and 2003, inclusive.

Methods

Data were obtained from requests to the Clinical Pathology Services of 23 hospitals and the National Institute of Health's delegation in Porto. Correspondence was received during the period between October 2003 and February 2004. Retrospective identification of cases of listeriosis during the previous decade was requested from each hospital. The contact person in each hospital was requested to complete a form containing the following information regarding each case: year of isolation, age and sex of the patient, factors that increased risk, the tissue or fluid origin of the isolate and the outcome of the infection. For the purposes of this study a case of listeriosis is defined as when clinical symptoms were consistent with a systemic infection with this organism and L. monocytogenes is isolated from a normally sterile site (usually blood or cerebrospinal fluid, or less commonly, joint, pleural, or pericardial fluid) or from placental or foetal tissue in the setting of miscarriage or stillbirth and. Approval by an Ethics Committee was not required.

Results

At least 35 cases were identified between 1994 and 2003 (Table 1). The highest annual number of cases was recorded for the year of 2003, this might be explained by the fact that the hospitals were contacted in October of that year and were obviously more vigilant in the detection and recording of this infection.
Table 1

Listeriosis in Portugal: 1994–2003

Date of isolation

Age†/Sex*†

Predisposing factors†

Clinical manifestations†

Isolated from†‡

Clinical outcome†

November 1994

New-born/M

Age

DNR

Liver

Fatal

1996

DNR/M

HIV

Fever

Blood and CSF

DNR

July 1997

DNR

DNR

DNR

Blood

DNR

September 1997

DNR

DNR

DNR

CSF

DNR

October 1997

DNR

DNR

DNR

CSF

DNR

1998

54/M

DNR

DNR

Blood

DNR

April 1998

DNR

DNR

DNR

CSF

DNR

January 1999

DNR

DNR

DNR

CSF

DNR

July 1999

DNR

DNR

DNR

CSF

DNR

September 1999

DNR

DNR

DNR

Blood

DNR

October 1999

New-born/F

Age

DNR

Lung

Fatal

2000

48/M

DNR

Fever and headache Stiff neck

CSF

DNR

2000

25/F

Pregnancy

Flu syndrome 15 days before birth

Vaginal culture

Birth at 36 weeks of pregnancy

2000

New-born/DNR

Age

Hypotonia, breath difficulties, sepsis at birth.

Apgar score 5 (1 min) – 7 (5 min)

Blood

Favourable without sequelae

March 2000

DNR

DNR

DNR

Blood

DNR

April 2000

DNR

DNR

DNR

Blood

DNR

June 2000

DNR

DNR

DNR

CSF

DNR

October 2000

DNR

DNR

DNR

Blood

DNR

May 2001

41/M

Cirrhosis

DNR

Blood

Fatal

October 2001

85/M

Age

DNR

Blood

Fatal

February 2002

DNR/M

DNR

Meningitis

CSF

DNR

March 2002

55/M

Haematological illness.

DNR

Blood

Favourable

2003

75/F

Chronic renal failure

DNR

Blood

Favourable

2003

New-born/DNR

Age

DNR

Blood

Favourable

2003

DNR/F

DNR

DNR

Vaginal culture

DNR

2003

DNR/F

DNR

DNR

Vaginal culture

DNR

January 2003

69/M

Age

DNR

Blood

Favourable

February 2003

74/F

Age

Meningitis

CSF

Favourable

February 2003

31/F

Pregnancy

DNR

Placenta

Favourable

April 2003

New-born/DNR

Age

DNR

Blood

Favourable without sequelae

April 2003

67/M

Corticosteroid therapy.

Nephritic syndrome

Meningitis

Blood, CSF and ascitic fluid

Fatal (Septic shock)

May 2003

25/M

DNR

Meningitis

CSF

DNR

July 2003

85/F

Age

DNR

CSF

DNR

October 2003

50/M

Alcoholism

DNR

Blood/CSF

Fatal

November 2003

48/M

DNR

DNR

CSF

With internment return but without sequelae

†DNR, Data not recorded.

*F, Female; M, Male.

‡CSF, cerebrospinal fluid.

The age of the patients, reported for 20 out of the 35 cases, varied between neonates (5 new-borns, 25%) and 85 years (6 older than 65 years, 30%), and were predominantly male (13 out of the 21 cases recorded, 62%). For 7 cases other malignancies were recorded and included; cirrhosis, haematological syndromes, alcoholism, chronic renal failure, nephritic syndrome and HIV infection (Table 1).

In the present study, even though the clinical symptoms were not recorded for the majority of cases, isolation of L. monocytogenes from blood (40%) and from cerebrospinal fluid (43%) was positive. The clinical signs described were meningitis, fever and sepsis at birth. The clinical outcome, recorded in 16 episodes, was fatal for 6 patients. Therefore the observed death rate must lie between 17% (6/35 – the total number of listeriosis episodes reported) and 37,5% (6/16 – the number of listeriosis episodes for which full case histories are available). Patients with a favourable clinical outcome apparently did not present any sequelae.

Discussion

According to the data collected in this study, the incidence of listeriosis was at least 1.4 cases per million inhabitants for the year 2003 considering the resident population of Portugal as that given by the National Institute of Statistics. This relatively low incidence must be considered with care because it is taken from a single year and the data gathered certainly cannot be considered exhaustive. Notification of listeriosis is not legally obligatory in Portugal. This, along with the fact that clinical symptoms are sometimes not evident, thus making diagnosis difficult, is an impediment to the gathering of more credible data [68]. Considering that not all of the country's healthcare units were contacted in this study, the national incidence rate presented here is, of necessity, an initial estimate.

From the recorded case data, L. monocytogenes was mainly isolated from blood and cerebrospinal fluid. It has been reported in a study with similar scope that, in cases where non-perinatal infection has led to clinical manifestations, primary bacteraemia was the most common cause (47%) followed by meningitis (28%) [7].

As reported for other countries, the majority of the cases were non-perinatal [7]. The case-fatality rate, similar to that reported in studies from other countries, 36% worldwide average for non-perinatal cases [7] and 40% for Spain [9], reflects the severity of the infection, in particular among new-borns and immunocompromised. As in previous studies, a predominance of the infection in males was verified [7, 8].

Conclusion

The study demonstrates, for the first time in the widely available literature, that despite their being no cases of listeriosis in Portugal recorded in official reports, the threat of L. monocytogenes to public health is of a similar dimension to that in other countries [3, 4].

It is highly likely that there will be a continued increase in the size of certain at-risk groups, namely the elderly and immunocompromised patients. The education of these and other, at-risk groups and of the professionals providing care for them, is proposed as a key strategy in the reduction of the incidence of listeriosis [10]. An example of this need is the fact that in a survey of 312 women that had been pregnant, only 54% changed their food habits during pregnancy (P. Teixeira, unpublished data).

Notes

Declarations

Acknowledgements

This study was supported by the Foundation Caloust Gulbenkian (project n° 49975) and by the FCT/FEDER (project POCTI/AGR/44889/2002).

Authors’ Affiliations

(1)
Escola Superior de Biotecnologia, Universidade Católica Portuguesa

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Copyright

© Almeida et al; licensee BioMed Central Ltd. 2006

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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