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International Scientific Forum on Home Hygiene


Background Information on Infectious Intestinal Disease
 in the home
- it’s not all foodborne!


What is IID?

Case definition of infectious intestinal disease (IID): people reporting diarrhoea or significant vomiting lasting less than 2 weeks, preceded by a symptom-free period of at least 3 weeks in the absence of a known non-infectious cause. Vomiting is considered significant if occurs more than once in a 24-hour period, incapacitates the person or is accompanied by other symptoms such as cramps or fever.

 IID diagnoses include intestinal infections resulting from bacteria and viruses, salmonellosis, shigellosis, food poisoning, amoebiasis, other protozoal intestinal diseases, cholera, typhoid and paratyphoid fevers.


IID can be caused by the consumption of contaminated food and water or it may be transmitted from person-to-person either directly or indirectly. Examples of indirect transmission are via hands, environmental surfaces or the airborne route (e.g. inhalation of aerosols from vomit).


How is IID transmitted in the home?

Some IID is attributable to the consumption of contaminated food and poor food hygiene. Indications are that a significant proportion of cases occurring in the community is transmitted by other means.  Surveillance studies together with the community IID study (discussed below) suggest that alternative routes of spread are particularly important for viral infections, which represent the major component of IID in the community. 


The WHO report that, of IID outbreaks in Europe during 1999 and 2000, 60% and 69% respectively were due to person-to-person spread.


From surveillance data of IID outbreaks in England and Wales from 1992-1998 it is estimated that

·         19% of Salmonella outbreaks are transmitted by other means

·         less than half of E. coli O157 outbreaks are foodborne

·         only 3% of reported NV outbreaks are foodborne; the remainder are due to person-to-person spread.


In Scotland, person-to-person spread was main mode of transmission in 76% of Norovirus IID outbreaks in 2002.


Food-borne IID can arise by consumption of food that has become contaminated during preparation for sale, or the food can become contaminated by an infected person in the home who handles and prepares food for the family


Person-to-person spread can occur by a number of means including direct contact between infected and uninfected family members or by inhalation of infected aerosol particles produced e.g. by vomiting.  For person-to-person spread of infection, hands and other surfaces can also play a significant part and these infections are preventable by good hygiene.


·         Carpets can harbour NV serving as reservoirs of infection. Two carpet fitters became ill after removing a carpet from a hospital ward 13 days after the last case in outbreak. Routine vacuuming every day since the outbreak had not removed the virus.

·         During a prolonged outbreak of NV gastroenteritis in a hotel, NV was detected on environmental sites such as carpets and toilet areas.

·         For E. coli 0157, the household secondary transmission rate from an index case is estimated at 4-14%. 

·         In an investigation of 50 homes in the US in which children under 4 years were known to be infected with Salmonella spp., Salmonella was recovered from 38% of homes. In all but 2 homes, the same serotype was isolated from the environment, another family member, or pets in the home. The study indicated that other risk factors were significant for development of salmonellosis in children other than contaminated foods.


IID reports in England and Wales during 2001



Number of reports









Norovirus (NV)


Escherichia coli





Other causes include Staphylococcus aureus, Bacillus spp., Shigella spp., Giardia spp. and adenovirus.


Reported General Outbreaks of IID

Note: a general outbreak is an outbreak that affects members of more than one household, or residents of an institution.








England and Wales



















It is calculated that of the total reported outbreaks of IID in England and Wales:

·         25% due to bacteria

·         38% due to viruses

·         36% unknown cause (although half suspected as viral)


Data from community IID study

A study involving 460,000 participants was carried out in England and Wales to evaluate IID cases in the community and presenting to general practice. The study indicated that: 

·         As many as 1 in 5 people in the general population develop IID each year

·         This gives an estimated 9.4 million cases each year 

·         For every one IID case detected by surveillance, another 136 cases occur in the community.

·         Only 1 in 6 patients consults a doctor. 

·         It is not possible to determine exactly what proportion of these cases originate in the home


The ratio of unreported cases in the community to cases reported to national surveillance was estimated:

·         For every 1 case of Campylobacter reported, another 7.6 cases occur in the community

·         For every 1 case of Salmonella reported, 3.2 cases occur in the community

·         For every 1 case of Rotavirus reported, 35 cases occur in the community

·         For every 1 case of NV reported, 1562 cases occur in the community


What this means for England and Wales is that, using the figures above for “reported” IID cases in 2001:



Number of reported faecal isolates in 2001

Ratio of actual: reported cases

Estimated number of cases in the community


















Consequences and costs of IID

·         Each year IID causes over 300 deaths and 35000 hospital admissions in England and Wales.

·         The cost of IID to the health sector in UK has been estimated at 226 million Euros. This includes GP visits, laboratory tests, prescriptions and hospital stays.

·         Additional societal costs such as lost productivity, travel and death amounts to almost 2 billion Euros as well as 13 million days sick leave.

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