I have an article in the current issue of The New Republic about how the AIDS epidemic has been more severe in the United States than other developed countries. When I started my reporting, I assumed that the experience of AIDS was basically the same in Western Europe, Australia and North America, and I was all primed to write a little dispatch about how each country’s different reporting and surveillance systems just made it look different.
But that wasn’t what I found. The differences in the epidemic are real. AIDS arrived in America earlier than other countries, spread faster and has lingered longer. History, demographics, and politics account for the difference better than methodological quirks do.
But that doesn’t mean the methodology doesn’t matter. AIDS is a complex disease—easy to contract, invisible to spread, expensive to treat—and each country has a slightly different way of tracking the virus’s transmission through its population. The question became how—and whether—we can make comparisons between countries in spite of these differences.
The first thing you notice about HIV statistics is how slippery they are. The Centers for Disease Control and Prevention’s AIDS surveillance says there were 46,268 diagnoses of HIV in 2010. The online Atlas provided by the CDC’s National Center for HIV/AIDS says there were 46,043.
It’s the same in Europe. Each country reports its own HIV statistics independently, then they’re gathered and re-reported by the European Centers for Disease Control. The Robert Koch Institute (Germany’s equivalent of the CDC) says 3,034 people were infected with HIV in Germany in 2008. The ECDC says it was 2,850.
These discrepancies are understandable given the nature of the virus and the systems we use to track it. Every country has its own national surveillance system. In the U.S. and the U.K., clinics that provide HIV testing and care sends their numbers up the chain (“we diagnosed five people with HIV this month, three of them were gay men, two were drug users…”). Germany, by contrast, doesn’t track every clinic, just a sample, and produces the nationwide figures by adjusting them for population every year.
Because people are often diagnosed with HIV years after they’re infected—if at all—and because it takes time for numbers to arrive at the central authorities, the statistics are constantly being updated (“backcalculated,” which sounds cooler, is what the epidemiologists call it) to reflect the number of infections, as opposed to the number of diagnoses, that occurred in any given year.
It gets even trickier when it comes to counting AIDS deaths. An “AIDS death,” as defined by the U.S. and the U.K., is “someone with AIDS who dies,” whether they die from AIDS-induced pneumonia or are hit by a bus. People who are never diagnosed with AIDS, who die in the up-to-10-years-long incubation period, aren’t included in the numbers. Germany only counts deaths that are actually caused by AIDS, but they have the same problem of non-diagnosis. All three countries produce estimates on top of the raw case data.
So how do they know how many people have HIV but aren’t diagnosed? Every once in a while, epidemiologists take 10,000 or so random blood samples and test them all. In the U.S., the U.K., and Germany, it turns out an estimated 20 percent of people infected with HIV don’t know it.
Even AIDS itself has a different definition depending on where you’re standing. In the U.S., AIDS is someone whose little virus-fighters, their CD4 cells, are below 200 per cubic mm of blood (normal is 500-1,500) or who is already showing symptoms. The WHO definition is anyone with a CD4 count below 350. In most European countries, you need to have an AIDS-related infection to be diagnosed with AIDS.
So there are a lot of good reasons why comparing the AIDS epidemic between countries isn’t perfect. The numbers keep getting tweaked and updated, and the assumptions and definitions plugged into them differ by time and place. Epidemiologist after epidemiologist tells me that comparing any statistic directly to another is probably unfair. You need to think of each number as a range, a window that takes into account the vicissitudes of measuring an invisible disease with differently calibrated surveillance systems, much of it before digital record-keeping. UNAIDS, which has data for every country from Andorra to Zimbabwe, simply rounds all the numbers to the nearest hundred and puts a ‘circa’ (~) at the beginning of them.
Caroline Sabin, a professor of medical statistics and epidemiology at University College London and my sherpa through these methodological Himalayas, is the first to tell me not to make apples to apples comparisons. ‘It’s more like Red Delicious to Granny Smith,’ she says.
So why did I just spend a whole article comparing these numbers to each other?
The first reason I feel comfortable doing this is the consistency and scale of the differences between countries. In 2010, the lowest reported number of AIDS deaths in the United States was 15,529. The highest estimate of German AIDS deaths was 550. The rates per 100,000 population are 6.1 and 0.5, respectively. Those numbers have been steady since the early 2000s.
The three countries under comparison—Britain, Germany and the United States—have functioning governments and dedicated systems for tracking and reporting statistics. Their epidemiologists attend the same conferences, they apply the same statistical methods and rigor to their back-calculations. The calibration and strength of these systems differ, I’m sure, but we’re not comparing Monaco and Malawi here. Even accounting for the different methodologies, and accepting that each number is a range rather than a precise figure, no one gave me any reason to believe that the British and German systems are under-estimating their AIDS statistics by hundreds of percentage points.
It’s also worth noting that the differences in the epidemic show up beyond the national surveillance systems. Sabin points me to cohort studies, surveys of people living with HIV, that also found higher death rates in the U.S. than the rest of the rich world. In the story I mention one that reported mortality rates in the United States four times those in Europe, and roughly equal to South Africa.
A 2013 review comparing the AIDS epidemic across the 33 richest countries in the world—the U.S., the E.U., Japan, etc.—found that one-third of people living with HIV in the developed world were in the United States. This is the story the data seems to tell, no matter how you ask it.
“The scale of the epidemic in the U.S. is much greater,” Sabin told me. “We can’t say precisely by how much, but that’s what the numbers seem to say.”
"Mwanzoni mwa mwaka huu, gazeti la The New Republic lilitoa makala kuhusu jinsi ""ugonjwa wa Ukimwi"" ulivyoenea zaidi katika nchi za Amerika kuliko nchi nyingine zilizositawi." Nilipokuwa nikifanya ripoti, nilidhani kwamba uzoefu wa UKIMWI ulikuwa sawa katika Ulaya Magharibi, Australia na Amerika ya Kaskazini, na nilikuwa tayari kuandika ripoti ndogo kuhusu jinsi kila nchi tofauti ya ripoti na mifumo ya ufuatiliaji ilifanya kuonekana tofauti. Lakini sikuwa hivyo nilivyogundua. Tofauti katika janga hilo ni halisi. Ukimwi ulifika Marekani mapema kuliko nchi nyingine, ukaenea haraka zaidi na umedumu kwa muda mrefu zaidi. Historia, idadi ya watu, na siasa hueleza tofauti hiyo vizuri zaidi kuliko mambo ya kipekee ya mbinu. Lakini hiyo haimaanishi kwamba mbinu si muhimu. Ukimwi ni ugonjwa tata - rahisi kuambukizwa, usioonekana kuenea, ghali kutibu - na kila nchi ina njia tofauti kidogo ya kufuatilia maambukizi ya virusi kupitia idadi yake ya watu. Swali likawa jinsi - na kama - tunaweza kufanya kulinganisha kati ya nchi licha ya tofauti hizi. Jambo la kwanza unaloliona kuhusu takwimu za UKIMWI ni jinsi zinavyoweza kupotea. Kituo cha Kudhibiti na Kuzuia Magonjwa (CDC) kinasema kuwa watu 46,268 waliambukizwa virusi vya Ukimwi mwaka 2010. Kwa mujibu wa Atlas ya Mtandao ya Marekani iliyotolewa na Kituo cha Kitaifa cha CDC cha Ukimwi na Ukimwi, idadi ya watu walioambukizwa ilikuwa 46,043. Ni sawa katika Ulaya. Kila nchi inaripoti takwimu zake za HIV kwa kujitegemea, kisha zinakusanywa na kuripotiwa tena na Vituo vya Ulaya vya Udhibiti wa Magonjwa. Taasisi ya Robert Koch (Kijerumani sawa na CDC) inasema watu 3,034 waliambukizwa virusi vya Ukimwi nchini Ujerumani mnamo 2008. Kulingana na ECDC, idadi hiyo ni zaidi ya 2,850. Tofauti hizo zinaeleweka kwa kuzingatia asili ya virusi na mifumo tunayotumia kuvifuatilia. Kila nchi ina mfumo wake wa ufuatiliaji wa kitaifa. "Kulingana na ripoti ya utafiti wa UK, ""Watu watano walipatikana na virusi vya Ukimwi mwezi huu, watatu kati yao walikuwa mashoga, wawili walikuwa watumiaji wa dawa za kulevya.""" Ujerumani, kinyume chake, haifuatili kila kliniki, ni sampuli tu, na inazalisha takwimu za kitaifa kwa kuzirekebisha kwa idadi ya watu kila mwaka. Kwa sababu watu mara nyingi wanagunduliwa na virusi vya Ukimwi miaka baada ya kuambukizwa - ikiwa hata wanagunduliwa - na kwa sababu inachukua muda kwa idadi kufika kwa mamlaka kuu, takwimu zinasasishwa kila wakati (kuhesabiwa nyuma, ambayo inasikika baridi, ndivyo wataalamu wa magonjwa ya kuambukiza wanavyoiita) ili kuonyesha idadi ya maambukizo, kinyume na idadi ya utambuzi, ambao ulitokea katika mwaka wowote. Ni vigumu hata zaidi kuhesabu vifo vya ukimwi. "Kifo cha UKIDDA, kama ilivyofafanuliwa na Marekani na Uingereza, ni ""mtu mwenye UKIDDA anayekufa, "" iwe wanakufa kutokana na nimonia inayosababishwa na UKIDDA au wanagongwa na basi." Watu ambao hawajawahi kugunduliwa na UKIMWI, ambao hufa katika kipindi cha kuota cha hadi miaka 10, hawajajumuishwa katika idadi hiyo. Ujerumani inahesabu vifo vinavyosababishwa na Ukimwi, lakini bado hakuna dalili za ugonjwa huo. Nchi zote tatu hutengeneza makadirio juu ya data ya kesi mbichi. Kwa hiyo wanajuaje ni watu wangapi walio na HIV lakini hawajatambuliwa? Wataalamu wa magonjwa ya kuambukiza huchukua sampuli za damu 10,000 au zaidi na kuzichunguza. Katika nchi kama Marekani, Uingereza na Ujerumani, asilimia 20 ya watu walioambukizwa virusi vya Ukimwi hawajui. Hata UKIMWI yenyewe una ufafanuzi tofauti ikitegemea mahali unapo. "Ugonjwa wa Ukimwi ni ugonjwa unaoathiri watu ambao ""vipande vya virusi vidogo vya virusi"" (CD4 cells) vyao viko chini ya 200 kwa kila mm3 ya damu (kiwango cha kawaida ni 500-1500) au ambao tayari wana dalili." WHO inatoa ufafanuzi wa mtu yeyote mwenye CD4 chini ya 350. Katika nchi nyingi za Ulaya, unahitaji kuwa na maambukizi yanayohusiana na Ukimwi ili kugunduliwa kuwa na Ukimwi. Kwa hiyo kuna sababu nyingi nzuri kwa nini kulinganisha janga la Ukimwi kati ya nchi si kamilifu. Nambari hizo huendelea kubadilishwa na kusasishwa, na dhana na ufafanuzi ulioingizwa ndani yao hutofautiana kulingana na wakati na mahali. Mtaalamu mmoja wa magonjwa ya kuambukiza baada ya mwingine ananiambia kwamba kulinganisha takwimu yoyote moja kwa moja na nyingine labda si haki. "Kila nambari inapaswa kuwa ""kiwango,"" na ""kiwango cha juu,"" na ""kiwango cha juu"" cha kipimo cha ugonjwa usioonekana na mifumo tofauti ya ufuatiliaji, na zaidi ya hayo kabla ya kuweka rekodi za dijiti." UNAIDS, ambayo ina data kwa kila nchi kutoka Andorra hadi Zimbabwe, tu rounded namba zote kwa mia ya karibu na kuweka <unk>circa<unk> (~) katika mwanzo wao. Caroline Sabin, profesa wa takwimu za matibabu na magonjwa ya kuambukiza katika Chuo Kikuu cha London, na sherpa wangu kupitia Himalayas hizi za mbinu, ni wa kwanza kuniambia nisifanye upimaji wa apples kwa apples. "Ni zaidi kama Red Delicious kwa Granny Smith", anasema. Kwa nini mimi tu kutumia makala nzima kulinganisha idadi hizi kwa kila mmoja? Sababu ya kwanza ninayojisikia vizuri kufanya hili ni uthabiti na kiwango cha tofauti kati ya nchi. Mwaka 2010 idadi ya watu waliokufa kutokana na ugonjwa huo ilikuwa 15,529 nchini Marekani. Takwimu za juu zaidi za vifo vya UKIMWI nchini Ujerumani ni 550. Kiwango cha watu 100,000 ni 6.1% na 0.5% kwa kila mwaka. Idadi hiyo imedumu tangu mwanzoni mwa miaka ya 2000. Nchi tatu chini ya kulinganisha - Uingereza, Ujerumani na Marekani - zina serikali zinazofanya kazi na mifumo ya kujitolea kwa kufuatilia na kuripoti takwimu. Wataalamu wao wa magonjwa ya kuambukiza huhudhuria mikutano ileile, hutumia mbinu zileile za takwimu na ukali katika mahesabu yao ya nyuma. Utaratibu na nguvu ya mifumo hii hutofautiana, nina hakika, lakini hatutofautisha Monaco na Malawi hapa. Hata kwa kuzingatia mbinu tofauti, na kukubali kwamba kila idadi ni mbalimbali badala ya takwimu sahihi, hakuna mtu alinipa sababu yoyote ya kuamini kwamba mifumo ya Uingereza na Ujerumani ni underestimating takwimu zao za UKIMWI na mamia ya pointi asilimia. Pia ni muhimu kutambua kwamba tofauti katika janga hilo zinaonekana zaidi ya mifumo ya kitaifa ya ufuatiliaji. Sabin alitoa utafiti wa watu walio na virusi vya Ukimwi ambao ulionyesha kuwa idadi ya watu wanaokufa nchini Marekani ni kubwa kuliko nchi nyingine tajiri. Katika ripoti hiyo, iliripotiwa kuwa kiwango cha vifo nchini Marekani ni mara nne ya kiwango cha Ulaya na karibu sawa na Afrika Kusini. Uchunguzi wa mwaka 2013 uliofananisha janga la Ukimwi katika nchi 33 tajiri zaidi duniani - Marekani, Ulaya, Japan, na kadhalika - uligundua kuwa theluthi moja ya watu wanaoishi na virusi vya Ukimwi katika nchi zilizoendelea walikuwa nchini Marekani. Hii ni hadithi ambayo data inaonekana kuwaambia, bila kujali jinsi unavyoiuliza. "Ukubwa wa janga hilo nchini Marekani ni mkubwa zaidi", Sabin aliniambia. "Hatuwezi kusema kwa usahihi kwa kiasi gani, lakini ndivyo namba zinavyoonekana kusema".