London faces a unique range and intensity of infectious disease problems due to the size, density, migration, ethnic diversity and international connectedness of its population. (The Office for National Statistics has reported extensively on London's population in its publication Focus on London.)

Infectious diseases of particular prominence in London include:

In London TB, sexually transmitted infectious, blood borne infections, meningococcal disease and food borne illnesses all continue to increase, with most of this burden carried by economically disadvantaged and socially deprived communities. Immunisation coverage for vaccine preventable childhood diseases (eg measles, mumps, whooping cough) have been falling in London in recent years and significant outbreaks are again beginning to occur. The capital remains particularly vulnerable to imported infections, ranging from malaria and tuberculosis to measles and haemorrhagic fevers. Recent events have shown that the risk of bioterrorism, debated by professionals for some years, is no longer just a theoretical possibility.

For more detailed information on infectious diseases in London, see the Reports section below.

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Infectious diseases (also known as communicable diseases) are caused by micro-organisms that are able to invade and reproduce in the human body, and then cause harmful effects. Many ('commensals') inhabit the body without harm. The most common types of infectious micro- organism are bacteria, viruses and parasites.

The global burden of infectious diseases is substantial, particularly in the developing world. In the developed world, advances in the last century in particular (including safe water supply and sewage disposal, advances in food hygiene, improvement in housing and general civic environments, use of immunisation and development of antibiotics) resulted in considerable reduction in the burden of infectious disease.

However, the developed world faces new challenges from infectious disease. More than twenty new infectious organisms have been identified since 1975, ranging from HIV and Hepatitis C to SARS, West Nile Virus and 'avian 'flu.' Some of these are undoubtedly 'old' organisms that have been newly identified (such as Hepatitis C). Others appear to be new entities, arising from genetic changes to organisms that were formerly confined to infecting animals (eg HIV, SARS). Other challenges arise from 'old diseases', formerly under control, regaining new currency eg tuberculosis, measles). The increased speed and frequency of global travel, as well as international political changes, offer new opportunities for well known diseases to increase in frequency in new populations. The ability of some micro-organisms to continually alter their genetic make-up through mutation means that new more infectious forms of 'old' diseases are always possible: influenza remains potentially capable of causing world wide pandemics.

A mobile, high density population with many areas of deprivation, high levels of migration, a multicultural population and frequent connections with countries worldwide, all combine to make London particularly vulnerable to both endemic and epidemic infectious disease. London, and similar metropolitan populations, therefore remain particularly vulnerable to these changes.

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Surveillance of infectious diseases in the United Kingdom is undertaken by the Health Protection Agency (HPA), formerly the Public Health Laboratory Service. The Agency has a regional network, responsible for regional infectious disease surveillance throughout England and Wales, which also supports national surveillance systems coordinated by the Communicable Disease Surveillance Centre, based in Colindale, North London.

HPA London supports the surveillance, prevention and control of communicable disease in greater London. This is achieved through coordination of a range of surveillance systems for monitoring the incidence and prevalence of infectious disease across the city. HPA London also provides information and technical advice to the NHS Regional Directors of Public Health, and to public health and health professionals and local authorities responsible for communicable disease control in the capital. These include communicable disease control consultants, clinicians, nurses, microbiologists and environmental health officers.

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TB is a serious but curable infectious disease caused by the tubercle bacterium. It can affect any part of the body but is most common in the lungs and lymph glands. Symptoms include cough, night sweats and weight loss. People with active TB affecting the lungs can infect others, but not all people with lung TB are infectious. The microscopic TB bacteria becomes airborne on tiny droplets of mucus and saliva produced when an infectious person talks, coughs or sneezes and others may then inhale these droplets. Most people who get TB have had a prolonged exposure to an infectious person, usually someone in the same household.

TB in the UK declined rapidly last century as antibiotics were introduced and gains were made of poverty and poor housing, but it never fully went away. Other parts of the world where treatment availability is very limited and poverty is a continuing problem still experience very high rates of infection. International campaigns act to improve treatment such as World TB day 2003.

The annual rate of TB in London increased from the late 1980s onwards, from just over 20 per 100,000 population in 1987 to 40 per 100,000 in 2001. By contrast the rates in England and Wales overall rose only slightly during this period, mainly as a result of the increasing numbers in the capital. In recent years London has accounted for about 40% of TB cases in the UK.

Treatment is very effective in curing TB but depends on prompt diagnosis and continuing treatment with more than one antibiotic over an extended period of time (usually six months). This can be difficult for those who are disadvantaged. London has extensive services aimed at supporting treatment in all social situations, such as the pan-London Tuberculosis Register and the London TB Nurses Network.

It is particularly important that London TB services work together to ensure that courses of TB treatment are completed. Taking anti-TB medication in the wrong dose, stopping and starting treatment or simply stopping treatment after a short time can result in the development of drug resistance. This makes the disease much harder to treat and significantly increases the sufferer's risk of long term complications or death. In 2000, laboratory data for the UK showed that 21% of Londoners with TB had tuberculosis which was resistant to at least one drug when they were first diagnosed. This compares to 13% in the rest of the UK.

The BCG immunisation can increase a persons immunity to TB and protect against the most severe forms of disease such as TB meningitis. BCG immunisation programmes vary across the UK according to the local risk of TB infection. In London, areas with particularly high incidence immunise all new born children. Otherwise, children are immunised between 10-14 years or at birth if their parents are from countries with high levels of TB.

For more information about TB, see the:

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Influenza is a highly contagious respiratory illness caused by the influenza virus, of which there are different strains which change rapidly. It is spread when a person breathes in droplets containing the virus breathed out by infected people. Flu is responsible for or contributes to a substantial number of deaths each year, particularly in the elderly or people whose immune systems are not working properly. Influenza causes a wide range of illness from minor symptoms through to pneumonia and death. Common symptoms include headache, fever, cough, sore throat, aching muscles and joints. It occurs most often in the winter months and usually peaks between December and March. Influenza activity during the last three winters in the UK has been relatively mild.

Most influenza illnesses resolve on their own with rest, plenty of fluids and painkillers taken as advised by a doctor or pharmacist. The National Institute for Clinical Excellence recommends the use of anti-viral treatment for those at risk of serious complications from flu.

Flu is a disease with rapid international spread. Extensive national and international surveillance and control activities have developed in response to this. The World Health Organisation publishes data about flu around the world in FluNet. They also lead on decisions about which strains of flu should go into the flu vaccine which has to be redesigned each year in response to the constantly changing flu virus.

The influenza vaccine is safe, and can be effective in reducing the severity of illness and reducing deaths from influenza infection. In the UK, influenza vaccine is recommended for all individuals aged 65 and over or in long stay residential care, as well as those with underlying health problems that put them at risk of complications from influenza. The influenza vaccine is safe, and can be effective in reducing the severity of illness and reducing deaths from influenza infection. In the UK, influenza vaccine is recommended for all individuals aged 65 and over or in long stay residential care, as well as those with underlying health problems that put them at risk of complications from influenza.

In London in 2001, 62% of people aged 65 or more had been immunised with influenza vaccine (compared with a national figure of 68%).

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Infectious diseases such as tetanus, polio, diphtheria, pertussis (whooping cough), Haemophilus influenzae (Hib), measles, mumps and rubella are all major causes of death and disability among children in the developing world. However, these infections have been largely controlled in the UK by the national immunisation schedule in childhood.

After clean water, vaccination is the most effective public health intervention in the world for saving lives and promoting good health. Vaccination is used to refer to all procedures for immunisation. (Immunisation is the process of protecting individuals from infection by giving (or increasing) a person's immunity to a disease either by introducing antibodies to the organism or by stimulating the immune system to produce it's own antibodies to the disease.)

The numbers of people receiving vaccination are monitored by the Department of Health's COVER program. Data is also collected on those falling ill from vaccine preventable disease. People who miss a specific vaccination are susceptible to that disease, and when enough people have missed their vaccinations, outbreaks of disease become much more likely. A high level of vaccination coverage is required and needs to be maintained every year as more children are born.

London's vaccine uptake has always been slightly lower than the rest of the UK, probably due to the mobility of the population, the complexity of the health service and local issues in surveillance system reporting. In recent years the uptake of immunisation against several vaccine preventable childhood diseases has declined nationwide, and London has additionally experienced some of the steepest falls. This decline in uptake has been most marked for the measles, mumps and rubella (MMR) vaccine, coinciding with a period of sustained adverse publicity surrounding its safety. As a result, London is again experiencing significant outbreaks of vaccine preventable disease, particularly measles.

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Meningococcal disease continues to be an important cause of death and disability in London, as elsewhere in England and Wales. At any one time the bacterium causing the disease, Neisseria meningitidis, can be found in the nose and throat of five to ten percent of the population. In nearly all cases this infection is harmless and self-limiting. Rarely, and for reasons still poorly understood, the bacterium is able to invade the body and cause systemic disease. Meningitis (inflammation of the lining of the brain) and septicaemia (bacterial blood poisoning) are the serious illnesses associated with this infection. This is a medical emergency and while the disease responds to early antibiotic treatment, intervention after signs of systemic infection have developed is less successful.

The incidence of meningococcal disease has fallen substantially in recent years largely due to the success of the meningococcal C vaccination programme introduced in 1999. Between this vaccine introduction and June 2002, Meningitis C cases fell by 87%, to just 15 cases in the first six months of 2002.

Group B disease, for which there is no vaccine, continues to be the most common form of meningococcal disease, with incidence rates remaining stable over the past three years. Management of these illnesses is therefore based on both use of serogroup C vaccine and early recognition of disease by doctors, parents and care-givers. During 2001 the overall case fatality rate for meningococcal disease cases in London was 5.9% (compared with 5.6% for England and Wales).

For more information about meningitis see the HPA section on meningitis and The Meningitis Research Foundation.

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Bacteria, viruses, protozoa, parasites and fungal contamination of food and water can all cause disease in humans, often characterised by diarrhoea. Viral illnesses such as hepatitis A (which often comes from contaminated water) and viral gastroenteritis from the Norwalk-like viruses continue to cause illness in England and Wales. Diarrhoeal illness caused by bacterial contamination of food and water contributes even more to the burden of infectious disease in England and Wales.

Of the bacterial infections, Campylobacter is the commonest reported cause of infectious intestinal disease in England and Wales. Common symptoms are severe diarrhoea and abdominal pain. Undercooked meat (especially poultry) is often associated with illness, as is unpasteurised milk and untreated water. There were 4018 identified cases reported in London in 2001.

Salmonella is the second most common cause of foodborne illness. Cases usually occur in single individuals, but sometimes outbreaks occur in the general population and in institutions such as schools and hospitals. Salmonella is passed on by ingestion of contaminated food, mainly of animal origin, or faecal contamination from an infected person or animal. Symptoms include watery and sometimes bloody diarrhoea, abdominal pain, headache, nausea, vomiting, and fever.

While notifications of these two diseases have been declining in the rest of England and Wales, the incidence in London and southern regions has remained steady or increased in recent years. The incidence of laboratory isolation of Salmonella in London is the highest in the country. The incidence of food poisoning within London is highest in boroughs south of the river, for reasons which are uncertain.

For more information on these and other organisms causing food and water related infectious disease please see the HPA website section on infectious diseases, and The Food Standards Agency and The Drinking Water Inspectorate.

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Some sexually transmitted infections (STIs) and bloodborne viruses (BBVs) can be transmitted both by sexual activity and via blood and blood products. These diseases are often grouped together for this reason.

For example, the human immunodeficiency virus (HIV) which causes AIDS can be transmitted either by sexual contact or via blood and blood products. People with HIV can have no symptoms for a long period before feeling unwell. There is no vaccine for HIV. Numbers of new cases of HIV infection continue to rise in the UK, with more than two thirds of cases in London. HIV prevalence is five times higher in gay men, eighttimes higher in heterosexual men and women and more than 15 times higher in injecting drug users (IDUs) in London compared with the rest of England and Wales.

London has been piloting a new surveillance scheme in recent years where women are offered the chance to be tested for a variety of diseases during pregnancy. Uptake of this antenatal screening for HIV has risen from 71% in 2000 to 83% in 2001, which increases the number of people able to make informed decisions about care for their child if they test positive. Extensive information on HIV/AIDS can be found at the HPA section on HIV and from the Terrence Higgins Trust.

Hepatitis B is another bloodborne and sexually transmitted virus. It causes inflammation of the liver. Many infected people have no symptoms, but others have a flu-like illness with nausea and jaundice. Hepatitis B vaccine can prevent hepatitis B infection. Hepatitis B infections are increasing among IDUs across the country, with London having a higher prevalence than other regions. Homosexual men are also disproportionately affected.

Diseases where transmission of infection is associated almost solely with sexual contact include the bacterial infections gonorrhoea, chlamydia and syphilis.

New diagnoses of gonorrhoea and genital chlamydia infection in London continue to rise. Genital Chlamydia trachomatis is the commonest STI in England, Wales and Northern Ireland. This infection is an important reproductive health problem, because 10-30% of infected women develop pelvic inflammatory disease (PID) which in turn may have implications for a woman's fertility. Gonorrhoea is the second most common STI. The highest rates are found in London and predominantly urban areas. Young women and Black Caribbean people in the capital are disproportionately affected by both gonorrhoea and chlamydia.

There was a resurgence of syphilis in London during 2000 and 2001 with an eight-fold increase in diagnoses in since 1996. This disease, which can have serious consequences for health such as dementia if not treated, had fallen to very low levels in London with the arrival of antibiotics. Diagnoses in males fell further in the early to mid-1980s, coinciding with emerging awareness of HIV, adoption of safer sex practices, and a parallel fall in HIV transmission among men who have sex with men. The resurgence in syphilis and other STIs is thought to reflect changes in sexual behaviour. Enhanced laboratory surveillance of infectious syphilis was introduced in London in 2001 and extended to the whole of England in June 2002.

For more information about HIV, Hepatitis B, Gonorrhoea, Chlamydia and Syphillis see the HPA website.

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Communicable diseases can be imported into the country via UK-residents who have recently travelled abroad, migrants entering the UK for short or long term study, work or holiday, and refugees or asylum seekers.

London is particularly vulnerable to imported infectious disease. The region has a wide diversity of ethnic populations and many members of these communities return regularly to their countries of origin for family, religious and holiday reasons. While abroad, they are at risk of contracting infection, as are those travelling for business and pleasure. One effect of these patterns of international travel is that reports of infections such as malaria commonly peak after the school holidays.

Additionally, the city has four of the UK's major international airports, as well as being the final destination for the Eurostar, receiving millions of travellers each year. London and the South-East have traditionally also been the first home for the majority of refugees and asylum seekers to the UK. Onward transmission of these so-called 'tropical diseases' is not common in the UK. Malaria for example relies on the bite of a female mosquito to transmit the infective agent Plasmodium and so non-travel related cases are very rare in the UK.

During 2001 more cases of infections associated with travel abroad were reported from London than any other region. Two thirds of malaria cases notified in England and Wales during 2001 were reported from London, and incidence increased in London between 2000 and 2001 in contrast to a decrease nationwide.

For more information about Malaria see the HPA website section on malaria and for malaria and other travel associated illness see the website of London's Hospital for Tropical Diseases.

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Infection arising during hospital or community based medical care is a problem of increasing magnitude in England and Wales. It affects both patients and hospital workers. Each year it is estimated that 8% of patients acquire an infection during their hospital admission. A further 19% of patients in the community are estimated to have infections associated with their recent hospital treatment. Consequences can be serious for those infected, with prolonged illness and/or recovery time in addition to their original illness, and sometimes death.

The rise in these infections is believed to be due to a combination of factors, including the widespread use of antibiotics and an associated increase in resistance to these by the organisms they target. Good hygiene and infection control procedures in hospital, with careful and appropriate use of antibiotics help to reduce the incidence of these infections.

One of the most common and serious infections is MRSA (Methicillin resistant Staphylococcus aureus). The bacteria Staphylococcus aureus usually lives harmlessly on skin and in the nose of a third of the population. However, if it enters a wound or medical device site it can cause local infections. In more serious cases, this infection spreads into the bloodstream to cause blood poisoning (bacteraemia). Such an infection is easily treated with antibiotics, but in the case of MRSA treatment is complicated by the organism's resistance to Methicillin, a type of penicillin and some other antibiotics.

The incidence of MRSA (Methicillin resistant Staphylococcus aureus) infection is increasing in England and Wales, with London among the five regions reporting the highest proportion of MRSA bacteraemias (positive blood cultures) during 2001. The Chief Medical Officer for England has published 'Winning Ways' which outlines plans to reduce healthcare associated infection in England.

For more information see the HPA website section on healthcare associated infection.

Date	Title	Format	View
8 Apr 2009	A vision and commissioning strategy for TB in London
31 Mar 2009	Tuberculosis in London 2007: a report from HPA London and NHS London
15 Nov 2007	Tuberculosis in the UK: annual report on tuberculosis surveillance and control in the UK 2007
1 Nov 2007	London and TB
1 Aug 2006	Communicable disease in London 2002-05
10 Jun 2005	Health Protection Agency - Annual Report and Accounts 2004
10 Jun 2005	Patient Environment Action Team 'Clean Hospitals' Programme Results
3 Aug 2004	London i: quarterly surveillance bulletin. Vol. 1, no. 4, Spring 2004
17 Dec 2003	Communicable disease in London 2001
17 Dec 2003	London i: quarterly surveillance bulletin. Vol. 1, no. 1, April 2003
17 Dec 2003	London i: quarterly surveillance bulletin. Vol. 1, no. 2, August 2003
17 Dec 2003	London i: quarterly surveillance bulletin. Vol. 1, no. 3, December 2003

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