Travel-associated infections in England, Wales and Northern Ireland: 2023
Updated 21 March 2024
Applies to England
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Background
This report, produced by the Travel Health and International Health Regulations (IHR) team in the Clinical and Emerging Infections Directorate, UK Health Security Agency (UKHSA), summarises case numbers of selected travel-associated infections reported in England, Wales and Northern Ireland (EWNI). The data presented in this report supersedes any other case numbers previously reported.
Detailed information is included on the trends of chikungunya, cholera, dengue, rickettsial infections and Zika in 2023. An infection summary and key findings are provided for Japanese encephalitis and yellow fever. Data presented here is collated from a variety of sources and may be subject to limitations in completeness due to various factors, including underreporting.
Detailed annual reports are available elsewhere for imported malaria cases in the UK and travel-associated enteric fever cases in EWNI.
Data sources
Data for cases of chikungunya, dengue, Japanese encephalitis, rickettsial infections, yellow fever and Zika was obtained from the Rare and Imported Pathogens Laboratory (RIPL), UKHSA Porton (1). Case definitions used for these infections are:
- confirmed: molecular detection (PCR, other molecular amplification test or sequencing) and/or positive virus isolation and/or seroconversion between acute and convalescent samples and/or four-fold rise in antibody titre
- probable: IgM and IgG positive and compatible clinical syndrome
Data for confirmed cholera cases was obtained from the UKHSA Gastrointestinal Bacteria Reference Unit (GBRU). A confirmed case is a person with Vibrio cholerae serogroup O1 or O139 confirmed by the GBRU (2).
For all cases, specimen collection date was used where available to conduct analysis. In cases where this information was not available, laboratory receipt date was used. Case numbers presented in this report include both confirmed and probable cases, collated from multiple sources, including confirmed cases from GBRU, and both confirmed and probable cases from RIPL.
Data for UK residents and UK overseas visitors was obtained using the International Passenger Survey (IPS) data provided to the Travel Health team by the Office of National Statistics (ONS). Further information and analysis for travel trends seen in 2022 were obtained from the ONS website (3).
World regions of travel were assigned based on the United Nations world region classifications (4).
Changes in travel to and from the UK in 2022
Data on travel to and from the UK, obtained from the ONS International Passenger Survey, represents the most up to date travel data currently available.
In 2022, UK residents made 71.0 million visits abroad, a four-fold increase compared to 2021 (19.1 million). There were 31.2 million visits made by overseas residents to the UK, a five-fold increase compared to 2021 (6.4 million). These increases can be attributed to the easing of COVID-19 travel restrictions at the end of 2021. However, travel to and from the UK in 2022 still remained below the pre-COVID-19 pandemic levels of 2019 (Figure 1) (5).
For both UK visits abroad and overseas visits to the UK in 2022, seasonality of travel returned to pre-COVID-19 patterns, with most travel in occurring during the summer and a peak in August.
The most popular reasons for travel by UK residents in 2022 were holidays, with 45.6 million visits, followed by visiting friends and relatives (19.0 million) and business travel (4.8 million). The top 5 most visited countries were Spain, France, Italy, Greece and Portugal.
Holiday travel was also the most popular reason for overseas residents visiting the UK in 2022, with 12.1 million visits, followed by visiting friends and relatives (11.8 million) and business travel (5.1 million). This is a change compared to 2021 when visiting friends and relatives was the most popular reason for travel to the UK. Residents of the USA, France, Republic of Ireland, Germany and Spain represented the highest numbers of overseas residents visiting the UK (3).
Figure 1. Visits to and from the UK: from 2013 to 2022
Travel-associated infections 2019 to 2023
Table 1. Travel-associated infections in England, Wales and Northern Ireland (EWNI): 2019 to 2023
| Disease (Organism)* | 2019 | 2020 | 2021 | 2022 | 2023 |
|---|---|---|---|---|---|
| Chikungunya | 100 | 33 | 17 | 31 | 45 |
| Cholera (Vibrio cholerae serogroup O1 or O139) | 15 | 2 | 2 | 20 | 17 |
| Dengue | 790 | 91 | 97 | 448 | 634 |
| Japanese encephalitis | – | – | – | – | 1 |
| Rickettsial infections | 39 | 12 | 4 | 31 | 42 |
| Yellow fever | – | – | – | – | – |
| Zika | 6 | 1 | 1 | 8 | 8 |
*Only includes confirmed and probable cases
Table 1 presents reported travel-associated infections in England, Wales, and Northern Ireland from 2019 to 2023. Dengue remains the most frequently reported infection, with cases increasing from 448 in 2022 to 634 in 2023. Similarly, there were increases in cases of chikungunya and rickettsial infections in 2023. The reasons for these trends are not clear and may reflect changes in ascertainment, testing patterns, as well as the burden of disease, global infectious disease epidemiology, clinician awareness and travel trends.
Chikungunya
Chikungunya is a mosquito-borne infection transmitted by the bite of an infected female Aedes mosquito and is caused by a virus from the Flaviviridae family. It is characterised by a sudden onset of fever usually accompanied by joint pain (arthralgia); however, symptoms vary in severity. Serious complications are uncommon, but, rarely, in older people the disease can contribute to the cause of death, particularly if there is other underlying illness. Chikungunya mainly occurs in Africa, Asia and specifically in Southern Asia, although there have been cases reported in parts of Europe and North America (6).
In EWNI, there were 45 chikungunya cases reported in 2023, all of which were from England. Of these, 25 (56%) were confirmed cases and 20 (44%) were probable cases. This represents a 45% increase compared to 2022 (n=31). Case numbers were lower in the first three quarters of 2023 (n=8, n=6, n=9) and the majority of cases (n=22) were diagnosed in the fourth quarter (Figure 2).
Figure 2. Cases of chikungunya by quarter, Q1 2019 to Q4 2023
In 2023, 28 cases (62%) were female (aged 13 to 77 years, median=43) and 17 (38%) were male (aged 31 to 71, median=48) (Figure 3).
Figure 3. Cases of chikungunya by age group and sex, 2023 (n=45)
In 2023, travel history was known for 43 out of 45 cases, with the majority of these reporting travel to Southern Asia (28, 65%) and South-Eastern Asia (5, 12%) (Table 2). The most frequently reported country of travel was India (28), followed by Brazil (3) and Nigeria (3).
Cases who travelled to India reported travelling to a number of regions including Punjab, Maharashtra, Delhi and Uttar Pradesh. India reported a 20% increase in chikungunya cases (confirmed and suspected) in 2023 compared to 2022 (7), including increases in Punjab and Uttar Pradesh, where EWNI cases reported travelling to. One case reported travelling to Argentina, making this the first report of travel to the country in data available since 2008 for chikungunya cases in EWNI.
Table 2. Cases of chikungunya by region of travel, 2023
| Region of travel | Number of cases |
|---|---|
| Southern Asia | 28 |
| South-Eastern Asia | 5 |
| Western Africa | 4 |
| South America | 4 |
| Caribbean | 1 |
| Eastern Africa | 1 |
| Not stated | 2 |
| Total* | 45 |
*Some cases travelled to more than one region; all regions are included here so the total may be higher than the actual number of cases.
Cholera (Vibrio cholerae serogroup O1 or O139)
Cholera is caused by infection of one of two serogroups of the Vibrio cholerae bacteria, serogroups O1 and O139.
Cholera is an acute diarrhoeal disease caused by ingestion of contaminated food or water. A vaccine is available but is only recommended for some travellers. Cases of cholera may be asymptomatic or have mild symptoms, including acute, profuse watery diarrhoea (‘rice water stools’) and vomiting, leading to dehydration. Some infections may progress to severe disease, and in extreme cases may result in death if untreated (8). In 2022, cases were reported in 44 countries. The disease occurs mainly in Africa and Asia, but sporadic cases have also been reported in other regions (9).
There were 17 cholera cases reported in 2023, all of which were reported in England. This was a large 15% decrease compared to 2022 where 20 cases were reported. Case numbers were highest in the third quarter (n=11) (Figure 4).
Figure 4. Cases of cholera by quarter, Q1 2019 to Q4 2023
In 2023, 6 cases (35%) were female (aged 31 to 69 years, median=50) and 11 (65%) were male (aged 1 to 72 years, median=51) (Figure 5).
Figure 5. Cases of cholera by age group and sex, 2023 (n=17)
In 2023, travel history was known for all cases, with the majority of these reporting travel to Southern Asia (10, 56%) and Western Asia (3, 17%) (Table 3).
The most frequently reported country of travel was Pakistan (7), followed by India (2), Iraq (2) and Kenya (2).
Cholera case numbers have continued to be high in recent years during the 7th global pandemic, with double the number of cases reported to WHO compared to 2021. In 2022, of the 44 countries that reported cases, 30 reported outbreaks and 7 countries across Africa and Asia had very large outbreaks with over 10,000 cases (9).
Table 3. Cases of cholera by region of travel, 2023
| Region of travel | Number of cases |
|---|---|
| Southern Asia | 10 |
| Western Asia | 3 |
| Eastern Africa | 2 |
| Central America | 1 |
| Northern Africa | 1 |
| South-Eastern Asia | 1 |
| Total* | 18 |
*Some cases travelled to more than one region; all regions are included here so the total may be higher than the actual number of cases.
Dengue
Dengue is a mosquito-borne infection transmitted by the bite of an infected female Aedes mosquito. It is caused by a virus from the Flaviviridae family and has four main serotypes: DEN-1, DEN-2, DEN-3 and DEN-4.
Illness is characterised by an abrupt onset of fever often accompanied by severe headache and pain behind the eyes, muscle pain, joint pains, nausea, vomiting, abdominal pain and loss of appetite; however, symptoms can range from mild or non-existent to severe.
Severe dengue is rare in travellers (10). Dengue is endemic in over 100 countries across Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. with sporadic autochthonous cases occurring in France, Italy and Spain within Europe (10, 11). Since the beginning of 2023, the World Health Organization (WHO) has reported a rise in both dengue cases and deaths in areas known for dengue risk and in regions previously considered dengue-free, with significant increases particularly noted in Asia and the Americas (12).
In EWNI, 634 dengue cases were reported in 2023 (603 in England, 23 in Wales and 8 in Northern Ireland), of which 576 (91%) were confirmed cases and 58 (9%) were probable cases. This represents a 42% increase compared to 2022 (n=448). The majority of cases were diagnosed in the latter half of the year, with 222 cases in third quarter and 254 in the fourth quarter (Figure 6).
Figure 6. Cases of dengue by quarter, Q1 2019 to Q4 2023
In 2023, 306 cases (48%) were female (aged 1 to 80 years, median=36) and 325 (51%) were male (aged 3 to 83, median=39) (Figure 7). Sex was not recorded for 3 cases.
Figure 7. Cases of dengue by age group and sex, 2023 (n=631)
In 2023, travel history was known for 579 out of 634 cases (91%), with the majority of cases reporting travel to Southern Asia (230, 40%) and South-Eastern Asia (137, 24%) (Table 4). India was the most frequently reported country both within Southern Asia and for all dengue cases, accounting for 146 cases. However, the total cases associated with travel to this region decreased by 7% compared to 2022.
In contrast, cases associated with travel to South-Eastern Asia, Central America and the Caribbean increased significantly by 163%, 260% and 288%, respectively, when compared to the previous year. Thailand (South-Eastern Asia) was the most reported country in its region and the second highest overall of dengue cases, with 78 cases. For Central America, Mexico was the most reported country, with 34 cases. In the Caribbean, Barbados and Jamaica were the most frequently reported countries, with 34 and 32 cases, respectively.
Notably, one EWNI case reported travel to southern Italy. Although autochthonous dengue has been reported sporadically in Europe, in 2023, France and Italy reported significant outbreaks of locally transmitted dengue cases. Spain has also reported cases of locally acquired dengue during the same period (11). Current global reports on dengue cases indicate a rising trend, due to factors including climate change, rising temperatures and flooding (13).
Table 4. Cases of dengue by region of travel, 2023
| Region of travel | Number of cases |
|---|---|
| Southern Asia | 230 |
| South-Eastern Asia | 137 |
| Caribbean | 93 |
| Central America | 54 |
| South America | 28 |
| Eastern Africa | 21 |
| Western Asia | 12 |
| Western Africa | 6 |
| Eastern Asia | 6 |
| Northern Africa | 5 |
| Middle Africa | 1 |
| Oceania | 1 |
| Southern Africa | 1 |
| Southern Europe | 1 |
| Asia unspecified | 1 |
| Not stated | 55 |
| Total* | 652 |
*Some cases travelled to more than one region; all regions are included here so the total may be higher than the actual number of cases.
Rickettsial infections
Rickettsial infections are a group of bacterial infections of the genera Orientia and Rickettsia, which are transmitted by different arthropod vectors, including ticks, mites, lice and fleas, to animals such as humans, dogs, cats and cattle. In general, the incubation period is between 6 to 14 days post infection and symptoms vary but may include fever, myalgia, headache, dry cough and rash (14, 15, 16).
Human rickettsial infections are classified into 3 main groups: spotted fever group, typhus group and scrub typhus group. Spotted fever group infections are caused by over 30 Rickettsia species such as Rickettsia africae, Rickettsia conorii sp., and Rickettsia rickettsii. They are transmitted by ticks and have a specific geographical distribution. Typhus group infections are composed of two organisms; Rickettsia typhi is transmitted to humans through flea faeces mostly in Asia, Africa and the Western Pacific. R. prowazekii is transmitted to humans through louse faeces and is associated with high density living with associated poor hygiene. Scrub typhus infections are mainly caused by Orientia tsutsugamushi and transmitted through the bite of infected mite larvae. They are endemic across Asia, the Western Pacific, South America and Africa and cause an estimated 1 million cases per year (15, 16).
In 2023, there were 42 cases of rickettsial infections reported in EWNI (38 in England, 3 in Wales and one in Northern Ireland), which is a 35% increase compared to 31 cases reported in 2022. Of these, 17 (40%) were confirmed cases and 25 (60%) were probable cases. Case numbers in 2023 were the highest in quarters 2 and 3 (n=12 and n=14) (Figure 8). Of the reported cases, there were 23 cases (55%) in the spotted fever group, 9 cases (21%) in the scrub typhus group and 10 cases (24%) in the typhus group.
Figure 8. Cases of rickettsial infections by quarter, Q1 2019 to Q4 2023
In 2023, age and sex were known for all cases. Of these, 23 cases (56%) were female (aged 6 to 67 years, median=35) and 19 (44%) were male (aged 21 to 77 years, median=52) (Figure 9).
Figure 9. Cases of rickettsial infections by age group and sex, 2023 (n=42)
In 2023, travel history was known for 41 out of 42 cases. Of these, the majority of spotted fever cases reported travel to Southern Africa (17, 68%) and Eastern Africa (4, 16%). Scrub typhus cases are tested only when travel to Southern Asia or South-Eastern Asia is reported, and of the cases in 2023, 7 cases (78%) travelled to Southern Asia and 2 cases (22%) travelled to South-Eastern Asia. Typhus group cases reported travel to multiple regions including South-Eastern Asia (3, 25%), Eastern Asia (2, 17%), Middle Africa (2, 17%) and Southern Europe (2, 17%) (Table 5).
For all cases of rickettsial infection, the most frequently reported country of travel was South Africa (17), followed by India (5) and Cameroon, Greece, Indonesia, Sri Lanka and Thailand with 2 cases reporting travel to each.
Table 5. Cases of rickettsial infection by region of travel and rickettsial group, 2023
| Region of travel | Scrub typhus | Spotted fever | Typhus group | Total number of cases |
|---|---|---|---|---|
| Southern Africa | – | 17 | – | 17 |
| Southern Asia | 7 | – | 1 | 8 |
| Eastern Africa | – | 4 | 2 | 6 |
| South-Eastern Asia | 2 | 1 | 3 | 6 |
| Middle Africa | – | – | 2 | 2 |
| Southern Europe | – | – | 2 | 2 |
| Western Africa | – | 1 | 1 | 2 |
| Northern Africa | – | 1 | – | 1 |
| Northern America | – | – | 1 | 1 |
| Not stated | – | 1 | – | 1 |
| Total* | 9 | 25 | 12 | 46 |
*Some cases travelled to more than one region; all regions are included here so the total may be higher than the actual number of cases.
Zika
Zika is a mosquito-borne infection transmitted by the bite of an infected female Aedes mosquito. It is caused by a virus from the Flaviviridae family. Less commonly, transmission can occur through sexual contact, congenitally from a pregnant woman to her foetus and though blood transfusion (17).
The majority of people with Zika infection do not develop symptoms. Those that do often have mild symptoms which can include fever, headache, malaise, joint and muscle pain, a rash, itching, conjunctivitis and swollen joints (18).
Serious complications are uncommon, however an infection with Zika is a cause of congenital Zika Syndrome (characterised by microcephaly and other congenital anomalies) and neurological complications such as Guillain-Barré Syndrome.
During 2015 to 2016, there was a large outbreak of Zika virus infection in the Americas and the Caribbean, leading to the first imported Zika cases in the UK. As of 2022, 89 countries across Africa, Europe, the Americas, South-East Asia and the Western Pacific have reported autochthonous Zika cases (19).
In 2023, there were 8 Zika cases reported, all of these from England, consistent with number of cases reported in 2022. Of cases reported in 2023, 7 (88%) were confirmed cases and one (12%) was classified as a probable case. Case numbers were highest in the last two quarters (n=3 and n=4) compared to the first two quarters (n=0 and n=1) of the year (Figure 10). Notably, among these cases, 1 case of congenital Zika syndrome (CZS) was reported, which was linked to a travel history to Thailand. This was the first case of congenital Zika syndrome diagnosed antenatally in the UK.
Figure 10. Cases of Zika by quarter, Q1 2019 to Q4 2023
In 2023, 5 cases (63%) were female (aged 25 to 40 years, median=31) and 3 (37%) were male (aged 34 to 67, median=67) (Figure 11).
Figure 11. Cases of Zika by age group and sex, 2023 (n=8)
In 2023, travel history was known for 7 out of 8 cases (88%), with most reporting travel to South-Eastern Asia (4, 57%) (Table 6). The most frequently reported country of travel was Thailand (n=3). Additionally, one case was linked to travel in Vietnam (n=1). There have been reported increases in Zika virus cases in Thailand and other parts of South-Eastern Asia, as well as among travellers returning from these regions (20, 21). Of the remaining 4 cases, 2 travelled to Southern Asia; one to Sri Lanka and the other to India and the Maldives. One case travelled to Barbados (Caribbean), while the travel country/region for the fourth case was not known.
Table 6. Cases of Zika by region of travel, 2023
| Region of travel | Number of cases |
|---|---|
| South-Eastern Asia | 4 |
| Southern Asia | 2 |
| Caribbean | 1 |
| Not stated | 1 |
| Total | 8 |
Other travel-associated infections
Japanese encephalitis
Japanese encephalitis (JE) is a vaccine preventable mosquito-borne infection transmitted by the bite of Culex species mosquitoes. It is a flavivirus from the Flaviviridae family and is transmitted via mosquitoes to humans from pigs and water birds. Japanese encephalitis is found in 24 countries in South-Eastern Asia and the Pacific, mainly in settings where humans live in close proximity to pigs and water birds. A vaccine is available; however this is only advised for travellers at increased risk of infection. Most people with JE do not develop symptoms but for those who do symptoms may include fever and headache or vomiting in children. Less than 1% of people develop severe disease, which is characterised by encephalitic symptoms such as disorientation, seizures, coma and paralysis and approximately 30% of these cases are fatal. For cases who survive, approximately 30% suffer long term cognitive, behavioural or neurological complications (22, 23).
There was 1 confirmed case of Japanese encephalitis reported in EWNI in 2023 who reported travel to multiple countries in South-Eastern Asia.
Yellow fever
Yellow fever is a vaccine preventable mosquito-borne infection transmitted by the bite of multiple species of infected mosquitoes, including Aedes and Haemogogus species. Yellow fever virus is a flavivirus from the Flaviviridae family. Yellow fever is endemic in all or parts of 47 countries in Africa and Central and South America.
The incubation period ranges from 3 to 6 days. Many people do not develop symptoms but for those who do, these may include fever, headache, nausea or vomiting, muscle pain (often with backache), and loss of appetite. Most people will make a full recovery after 3 to 4 days; however, a small number (approximately 15%) will progress to a second phase of the infection and go on to develop jaundice, abdominal pain, renal failure and haemorrhage (bleeding). Up to half of infections in cases who develop severe symptoms may result in death. Yellow fever is rare in international travellers as there is a safe and effective vaccine available. Although the vaccine is safe, there have been reports of rare adverse events associated with its use (24).
In EWNI there were no cases of yellow fever reported in 2023. The most recently reported case in EWNI was in 2018.
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