Human cases were first identified in 1970 in Zaire (now known as the Democratic Republic of Congo, or DRC). Since then, cases have been increasing in humans, particularly in the DRC, which has reported cases continuously over that time. This increase in cases may be due to cessation of smallpox vaccination (which provided some cross-protection) or waning immunity, environmental factors (e.g., increased population density, human settlements in unknown animal reservoirs, deforestation), and/or genetic evolution of the virus. However, there is no evidence to support these theories.[4]Bunge EM, Hoet B, Chen L, et al. The changing epidemiology of human monkeypox – a potential threat? A systematic review. PLoS Negl Trop Dis. 2022 Feb;16(2):e0010141.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8870502
http://www.ncbi.nlm.nih.gov/pubmed/35148313?tool=bestpractice.com
[5]Beer EM, Rao VB. A systematic review of the epidemiology of human monkeypox outbreaks and implications for outbreak strategy. PLoS Negl Trop Dis. 2019 Oct;13(10):e0007791.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6816577
http://www.ncbi.nlm.nih.gov/pubmed/31618206?tool=bestpractice.com
[6]Nguyen PY, Ajisegiri WS, Costantino V, et al. Reemergence of human monkeypox and declining population immunity in the context of urbanization, Nigeria, 2017-2020. Emerg Infect Dis. 2021 Apr;27(4):1007-14.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8007331
http://www.ncbi.nlm.nih.gov/pubmed/33756100?tool=bestpractice.com
The disease is endemic in Central and Western Africa. The majority of cases have been reported in rural areas (adjacent to or within tropical forests) of the Congo Basin and western Africa, particularly in the DRC where a major outbreak occurred from 1996 to 1997.[5]Beer EM, Rao VB. A systematic review of the epidemiology of human monkeypox outbreaks and implications for outbreak strategy. PLoS Negl Trop Dis. 2019 Oct;13(10):e0007791.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6816577
http://www.ncbi.nlm.nih.gov/pubmed/31618206?tool=bestpractice.com
Between 2000 to 2021, there were 95 suspected and 40 confirmed outbreaks in the Central African Republic, with the number of outbreaks increasing after 2018.[8]Besombes C, Mbrenga F, Schaeffer L, et al. National monkeypox surveillance, Central African Republic, 2001-2021. Emerg Infect Dis. 2022 Nov 3;28(12).
http://www.ncbi.nlm.nih.gov/pubmed/36328951?tool=bestpractice.com
Nigeria experienced a reemergence of cases caused by the Clade II virus in 2017 after 39 years without reports of cases. Since then, five outbreaks have occurred between 2017 and 2021.[9]McCollum AM, Shelus V, Hill A, et al. Epidemiology of human mpox: worldwide, 2018-2021. MMWR Morb Mortal Wkly Rep. 2023 Jan 20;72(3):68-72.
https://www.cdc.gov/mmwr/volumes/72/wr/mm7203a4.htm
http://www.ncbi.nlm.nih.gov/pubmed/36656790?tool=bestpractice.com
There is currently an ongoing global outbreak, which was first identified in May 2022. Clusters of cases were reported across several countries outside of Africa with no direct travel links to an endemic area. This was the first time that chains of transmission were reported in countries without known epidemiological links to West and Central Africa.
Since the beginning of 2022, over 84,000 confirmed cases have been reported globally from 110 countries with 81 deaths, as of 20 January 2023. The number of cases peaked in August 2022 and has since been steadily declining. The most affected countries include the US, Brazil, Spain, France, and Colombia.[7]World Health Organization. 2022 mpox (monkeypox) outbreak: global trends. January 2023 [internet publication].
https://worldhealthorg.shinyapps.io/mpx_global
Cases have predominantly been in younger adult men, most of whom identify as gay, bisexual, or other men who have sex with men.[10]León-Figueroa DA, Barboza JJ, Garcia-Vasquez EA, et al. Epidemiological situation of monkeypox transmission by possible sexual contact: a systematic review. Trop Med Infect Dis. 2022 Sep 27;7(10):267.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9607952
http://www.ncbi.nlm.nih.gov/pubmed/36288008?tool=bestpractice.com
[11]Kumar R, Singh S, Singh SK. A systematic review of 5110 cases of monkeypox: what has changed between 1970 and 2022? Cureus. 2022 Oct;14(10):e30841.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9704117
http://www.ncbi.nlm.nih.gov/pubmed/36451652?tool=bestpractice.com
[12]Liu Q, Fu L, Wang B, et al. Clinical characteristics of human mpox (monkeypox) in 2022: a systematic review and meta-analysis. Pathogens. 2023 Jan 15;12(1):146.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9861547
http://www.ncbi.nlm.nih.gov/pubmed/36678494?tool=bestpractice.com
Males aged between 18 and 44 years are disproportionately affected.[7]World Health Organization. 2022 mpox (monkeypox) outbreak: global trends. January 2023 [internet publication].
https://worldhealthorg.shinyapps.io/mpx_global
Cases have also been reported in women (mainly heterosexual, including pregnant women) and children, albeit more rarely.[13]Grothe JH, Cornely OA, Salmanton-García J, et al. Monkeypox in children and adult women in Europe: results from a flash VACCELERATE pilot survey. Enferm Infecc Microbiol Clin. 2022 Sep 19 [Epub ahead of print].
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9534071
http://www.ncbi.nlm.nih.gov/pubmed/36249472?tool=bestpractice.com
[14]Vallejo-Plaza A, Rodríguez-Cabrera F, Hernando Sebastián V, et al. Mpox (formerly monkeypox) in women: epidemiological features and clinical characteristics of mpox cases in Spain, April to November 2022. Euro Surveill. 2022 Dec;27(48):2200867.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9716644
http://www.ncbi.nlm.nih.gov/pubmed/36695461?tool=bestpractice.com
[15]Gaeta F, De Caro F, Franci G, et al. Monkeypox infection 2022: an updated narrative review focusing on the neonatal and pediatric population. Children (Basel). 2022 Nov 26;9(12):1832.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9776986
http://www.ncbi.nlm.nih.gov/pubmed/36553276?tool=bestpractice.com
In the US, 2.7% of all reported cases were in women including 3% in pregnant or recently pregnant women (as of November 2022).[16]Oakley LP, Hufstetler K, O'Shea J, et al. Mpox cases among cisgender women and pregnant persons: United States, May 11 - November 7, 2022. MMWR Morb Mortal Wkly Rep. 2023 Jan 6;72(1):9-14.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9815154
http://www.ncbi.nlm.nih.gov/pubmed/36602932?tool=bestpractice.com
Transgender and gender-diverse people have been disproportionately affected during the outbreak.[17]Blackburn D, Roth NM, Gold JAW, et al. Epidemiologic and clinical features of mpox in transgender and gender-diverse adults: United States, May - November 2022. MMWR Morb Mortal Wkly Rep. 2022 Dec 30;71(5152):1605-9.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9812441
http://www.ncbi.nlm.nih.gov/pubmed/36580418?tool=bestpractice.com
Since the beginning of 2022, 1214 confirmed cases and 15 deaths have been reported in Africa as part of the outbreak, as of 20 January 2023. This represents 1% and 19% of global cases and deaths, respectively. Demographics of cases have been similar to recent previous outbreaks in Africa, but significantly different from other regions (65% of cases are in males with a median age of 25 years, and there are no data on sexual transmission).[7]World Health Organization. 2022 mpox (monkeypox) outbreak: global trends. January 2023 [internet publication].
https://worldhealthorg.shinyapps.io/mpx_global
Current epidemiological updates are available from public health authorities.
The median age at presentation has evolved from young children (4 years) in the 1970s to young adults (21 years) between 2010 and 2019.[4]Bunge EM, Hoet B, Chen L, et al. The changing epidemiology of human monkeypox – a potential threat? A systematic review. PLoS Negl Trop Dis. 2022 Feb;16(2):e0010141.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8870502
http://www.ncbi.nlm.nih.gov/pubmed/35148313?tool=bestpractice.com
In the 2022 global outbreak, cases have been uncommon in children compared with adults.[11]Kumar R, Singh S, Singh SK. A systematic review of 5110 cases of monkeypox: what has changed between 1970 and 2022? Cureus. 2022 Oct;14(10):e30841.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9704117
http://www.ncbi.nlm.nih.gov/pubmed/36451652?tool=bestpractice.com
[15]Gaeta F, De Caro F, Franci G, et al. Monkeypox infection 2022: an updated narrative review focusing on the neonatal and pediatric population. Children (Basel). 2022 Nov 26;9(12):1832.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9776986
http://www.ncbi.nlm.nih.gov/pubmed/36553276?tool=bestpractice.com
For example, in the US, children and adolescents aged <18 years represented 0.3% of all cases and none resulted in critical illness or death.[18]Hennessee I, Shelus V, McArdle CE, et al. Epidemiologic and clinical features of children and adolescents aged <18 years with monkeypox: United States, May 17 - September 24, 2022. MMWR Morb Mortal Wkly Rep. 2022 Nov 4;71(44):1407-11.
https://www.cdc.gov/mmwr/volumes/71/wr/mm7144a4.htm
http://www.ncbi.nlm.nih.gov/pubmed/36331124?tool=bestpractice.com
Available data from the 2022 global outbreak indicated that 28% to 51% of patients have been HIV-positive (in cases where HIV status is known).[19]Centers for Disease Control and Prevention. Clinical considerations for treatment and prophylaxis of mpox in people who are immunocompromised. January 2023 [internet publication].
https://www.cdc.gov/poxvirus/monkeypox/clinicians/people-with-HIV.html
[20]O'Shea J, Filardo TD, Morris SB, et al. Interim guidance for prevention and treatment of monkeypox in persons with HIV infection: United States, August 2022. MMWR Morb Mortal Wkly Rep. 2022 Aug 12;71(32):1023-8.
https://www.cdc.gov/mmwr/volumes/71/wr/mm7132e4.htm
http://www.ncbi.nlm.nih.gov/pubmed/35951495?tool=bestpractice.com
Although women account for a minority of cases, the proportion of women with HIV has been estimated to be 27% (50% in transgender women).[21]Thornhill JP, Palich R, Ghosn J, et al. Human monkeypox virus infection in women and non-binary individuals during the 2022 outbreaks: a global case series. Lancet. 2022 Dec 3;400(10367):1953-65.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(22)02187-0/fulltext
http://www.ncbi.nlm.nih.gov/pubmed/36403584?tool=bestpractice.com
However, in the largest study of women to date, only 4.4% of women had HIV (compared with 40.8% in men).[14]Vallejo-Plaza A, Rodríguez-Cabrera F, Hernando Sebastián V, et al. Mpox (formerly monkeypox) in women: epidemiological features and clinical characteristics of mpox cases in Spain, April to November 2022. Euro Surveill. 2022 Dec;27(48):2200867.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9716644
http://www.ncbi.nlm.nih.gov/pubmed/36695461?tool=bestpractice.com
Prior to the 2022 global outbreak, a small number of travel-associated cases had been reported in the UK, the US, Singapore, and Israel.[22]UK Health Security Agency. Monkeypox case in England. December 2018 [internet publication].
https://www.gov.uk/government/news/monkeypox-case-in-england
[23]UK Health Security Agency. Monkeypox case confirmed in England. December 2019 [internet publication].
https://www.gov.uk/government/news/monkeypox-case-confirmed-in-england
[24]World Health Organization. Monkeypox: United Kingdom of Great Britain and Northern Ireland. July 2021 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/monkeypox---united-kingdom-of-great-britain-and-northern-ireland
[25]World Health Organization. Monkeypox: United Kingdom of Great Britain and Northern Ireland. June 2022 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON381
[26]Centers for Disease Control and Prevention. Imported monkeypox case reported in Maryland. November 2021 [internet publication].
https://www.cdc.gov/media/releases/2021/s1117-monkeypox.html
[27]Centers for Disease Control and Prevention. CDC and Texas confirm monkeypox in U.S. traveler. July 2021 [internet publication].
https://www.cdc.gov/media/releases/2021/s0716-confirm-monkeypox.html
[28]Rao AK, Schulte J, Chen TH, et al. Monkeypox in a traveler returning from Nigeria – Dallas, Texas, July 2021. MMWR Morb Mortal Wkly Rep. 2022 Apr 8;71(14):509-16.
https://www.cdc.gov/mmwr/volumes/71/wr/mm7114a1.htm
http://www.ncbi.nlm.nih.gov/pubmed/35389974?tool=bestpractice.com
[29]World Health Organization. Disease outbreak news. Monkeypox - Singapore. May 2019 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/16-may-2019-monkeypox-singapore-en
[30]Erez N, Achdout H, Milrot E, et al. Diagnosis of imported monkeypox, Israel, 2018. Emerg Infect Dis. 2019 May;25(5):980-3.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6478227
http://www.ncbi.nlm.nih.gov/pubmed/30848724?tool=bestpractice.com
An outbreak of over 70 cases occurred in the US Midwest in 2003, and was the first reported occurrence of the disease outside of Africa. The source of this outbreak was exposure to infected prairie dogs that had acquired the infection from Gambian rats imported from West Africa.[31]Huhn GD, Bauer AM, Yorita K, et al. Clinical characteristics of human monkeypox, and risk factors for severe disease. Clin Infect Dis. 2005 Dec 15;41(12):1742-51.
https://academic.oup.com/cid/article/41/12/1742/344953
http://www.ncbi.nlm.nih.gov/pubmed/16288398?tool=bestpractice.com