Infectious Diseases - Hiv/aids

AIDS is the late stage of an infection caused by HIV, a retrovirus that attacks and destroys certain white blood cells, which weakens the body's immune system and makes it susceptible to infections and diseases that ordinarily would not be life threatening. AIDS is considered a bloodborne, sexually transmitted disease because HIV is spread through contact with blood, semen, or vaginal fluids from an infected person.

Around the World

AIDS and HIV were virtually unknown before 1981, when testing and reporting of the disease became mandatory, but awareness grew as the annual number of diagnosed cases and deaths steadily increased. By the end of 2003, approximately forty million people worldwide were estimated to be living with HIV/AIDS, according to the Joint United Nations Programme on HIV/AIDS (UNAIDS) and the WHO. Of those infected, 37.5 million were adults and about 2.5 million were children younger than age fifteen. Seventy percent of people infected with HIV lived in sub-Saharan Africa. In 2003, an estimated 26.6 million people in this region were living with HIV, including the 3.2 million who became infected during the previous year. AIDS killed approximately 2.3 million people in 2003 there. Unlike women in other regions in the world, African women are much more likely (about twice as much) than men to be infected with HIV.

Since the epidemic began, 21.8 million people have died of AIDS; an estimated three million died in 2003 alone. Of those, approximately 700,000 were children younger than fifteen years of age.

TABLE 7.3
Reported tuberculosis cases, 2001

	Tuberculosis cases				Tuberculosis deaths
			Percent change				Percent change
Year	Number	Rate1	Number	Rate	Number	Rate1	Number	Rate
1953	84,304	53.0	–	–	19,707	12.4	–	–
1954	79,775	49.3	−5.4	−7.0	16,527	10.2	−16.1	−17.7
1955	77,368	46.9	−3.0	−4.9	15,016	9.1	9.1	−10.8
1956	69,895	41.6	−9.7	−11.0	14,137	8.4	−5.9	−7.7
1957	67,149	39.2	−3.9	−5.8	13,390	7.8	−5.3	−7.1
1958	63,534	36.5	−5.4	−6.9	12,417	7.1	−7.3	−9.0
1959	57,535	32.5	−9.4	−11.0	11,474	6.5	−7.6	−8.5
1960	55,494	30.8	−3.5	−5.2	10,866	6.0	−5.3	−7.7
1961	53,726	29.4	−3.2	−4.5	9,938	5.4	−8.5	−10.0
1962	53,315	28.7	−0.8	−2.4	9,506	5.1	−4.3	−5.6
1963	54,042	28.7	+1.4	0.0	9,311	4.9	−2.1	−3.9
1964	50,874	26.6	−5.9	−7.3	8,303	4.3	−10.8	−12.2
1965	49,016	25.3	−3.7	−4.9	7,934	4.1	−4.4	−4.7
1966	47,767	24.4	−2.5	−3.6	7,625	3.9	−3.9	−4.9
1967	45,647	23.1	−4.4	−5.3	6,901	3.5	−9.5	−10.3
1968	42,623	21.3	−6.6	−7.8	6,292	3.1	−8.8	−11.4
1969	39,120	19.4	−8.2	−8.9	5,567	2.8	−11.5	−9.7
1970	37,137	18.3	−5.1	−5.7	5,217	2.6	−6.3	−7.1
1971	35,217	17.1	−5.2	−6.6	4,501	2.2	−13.7	−15.4
1972	32,882	15.8	−6.6	−7.6	4,376	2.1	−2.8	−4.5
1973	30,998	14.8	−5.7	−6.3	3,875	1.8	−11.4	−14.5
1974	30,122	14.2	−2.8	−4.1	3,513	1.7	−9.3	−5.6
1975	33,989	15.9	–	–	3,333	1.6	−5.1	−5.9
1976	32,105	15.0	−5.5	−5.7	3,130	1.5	−6.1	−6.3
1977	30,145	13.9	−6.1	−7.3	2,968	1.4	−5.2	−6.7
1978	28,521	13.1	−5.4	−5.8	2,914	1.3	−1.8	−7.1
1979	27,669	12.6	−3.0	−3.8	2,0072	0.92	31.12	−30.82
1980	27,749	12.3	+0.3	−2.4	1,978	0.9	−1.4	0.0
1981	27,373	11.9	−1.4	−3.3	1,937	0.8	−2.1	−11.1
1982	25,520	11.0	−6.8	−7.6	1,807	0.8	−6.7	0.0
1983	23,846	10.2	−6.6	−7.3	1,779	0.8	−1.5	+0.0
1984	22,255	9.4	−6.7	−7.8	1,729	0.7	−2.8	−12.5
1985	22,201	9.3	−0.2	+1.1	1,752	0.7	+1.3	0.0
1986	22,768	9.4	+2.6	−1.1	1,782	0.7	+1.7	0.0
1987	22,517	9.3	−1.1	−1.1	1,755	0.7	−1.5	0.0
1988	22,436	9.1	−0.4	−2.2	1,921	0.8	+9.5	+14.3
1989	23,495	9.5	+4.7	+4.4	1,970	0.8	+2.6	0.0
1990	25,701	10.3	+9.4	+8.4	1,810	0.7	−8.1	−12.5
1991	26,283	10.4	+2.3	+1.0	1,713	0.7	−5.4	0.0
1992	26,673	10.5	+1.5	+1.0	1,705	0.7	−0.5	0.0
1993	25,287	9.8	−5.2	−6.7	1,631	0.6	−4.3	−14.3
1994	24,361	9.4	−3.7	−4.1	1,478	0.6	−9.4	0.0
1995	22,860	8.7	−6.2	−7.4	1,336	0.5	−9.6	−16.7
1996	21,337	8.0	−6.7	+8.0	1,202	0.5	−10.0	0.0
1997	19,851	7.4	−7.0	−7.5	1,166	0.4	−3.0	−20.0
1998	18,361	6.8	−7.5	−8.1	1,112	0.4	−4.6	−0.0
1999	17,531	6.4	−4.5	−5.9	930	0.3	−16.4	−25.0
2000	16,377	5.8	−6.6	−9.4	7513	0.33	−19.23	−0.03
2001	15,989	5.6	−2.4	−3.4	–	–	–	–
1Per 100,000 population.
2The large decrease in 1979 occured because late effects of tuberculosis (e.g., bronchiectasis or fibrosis) and pleurisy with effusion (without mention of cause) are no longer included in tuberculosis deaths.
3Preliminary data obtained from National Center for Health Statistics (NCHS) National Vital Statistics Report, Vol. 49, No. 12, October 9, 2001.
Ellipses indicate data not available.
Note: Official tuberculosis mortality statistics are compiled by the National Center for Health Statistics, CDC. Case data after 1974 are not comparable to prior years due to changes in the surveillance case definitions which became effective in 1975.
SOURCE: "Reported Tuberculosis in the United States, 2001," U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Hyattsville, MD, September, 2002 [Online] http://www.cdc.gov/nchstp/tb/surv/surv2001/pdf/t1.pdf [accessed January 31, 2004]

In the United States

According to the CDC, by December 2002 there were 384,906 people in the United States living with AIDS. Of all cases of HIV infection in 2001, 39 percent progressed to AIDS within twelve months after the diagnosis of HIV infection. Diagnoses of HIV/AIDS in the United States increased 3.2 percent from 2001 (25,643) through 2002 (26,464). However, from 1998 to 2002 the estimated number of deaths among people with AIDS declined 14 percent as a result of highly active antiretroviral therapy that became widespread during 1996.

In 2002, 71 percent of all individuals with HIV in the reporting areas in the United States were male. However, worldwide, AIDS was more evenly divided between men

TABLE 7.4
AIDS cases, by persons' age category, exposure category, and sex, through December 2002

	Males				Females				Totals
	2002		Cumulative through 20021		2002		Cumulative through 20021		2002		Cumulative through 20021
Exposure category	No.	%	No.	%	No.	%	No.	%	No.	%	No.	%
Adult or adolescent
Male-to-male sexual contact	14,545	45	384,784	55	0	0	0	0	14,545	33	384,784	45
Injection drug use	5,121	16	151,367	22	2,381	21	58,552	39	7,502	17	209,920	25
Male-to-male sexual contact and injection drug use	1,510	5	54,224	8	0	0	0	0	1,510	3	54,224	6
Hemophilia/coagulation disorder	79	0	5,067	1	11	0	304	0	90	0	5,371	1
Heterosexual contact	3,213	10	36,692	5	4,740	42	63,379	42	7,953	18	100,071	12
Sex with injection drug user	519	2	10,412	1	985	9	22,939	15	1,504	3	33,351	4
Sex with bisexual male	0	0	0	0	205	2	4,088	3	205	0	4,088	0
Sex with person with hemophilia	3	0	72	0	15	0	446	0	18	0	518	0
Sex with HIV-infected transfusion recipient	27	0	472	0	32	0	660	0	59	0	1,132	0
Sex with HIV-infected person, risk not specified	2,664	8	25,736	4	3,503	31	35,246	23	6,167	14	60,982	7
Receipt of blood transfusion, blood components, or tissue2	147	0	5,164	1	118	1	3,988	3	265	1	9,152	1
Other/risk not reported or identified3	7,898	24	60,420	9	4,029	36	25,837	17	11,927	27	86,258	10
Subtotal	32,513	100	697,718	100	11,279	100	152,060	100	43,792	100	849,780	100
Child (13 yrs)
Hemophilia/coagulation disorder	0	0	229	5	0	0	7	0	0	0	236	3
Mother with, or at risk for, HIV infection	61	85	4,179	88	78	91	4,246	95	139	88	8,425	91
Injection drug use	5	7	1,637	35	7	8	1,622	36	12	8	3,259	35
Sex with injection drug user	4	6	771	16	5	6	735	16	9	6	1,506	16
Sex with bisexual male	3	4	95	2	5	6	100	2	8	5	195	2
Sex with person with hemophilia	1	1	19	0	0	0	15	0	1	1	34	0
Sex with HIV-infected transfusion recipient	0	0	11	0	0	0	14	0	0	0	25	0
Sex with HIV-infected person, risk not specified	21	29	679	14	26	30	718	16	47	30	1,397	15
Receipt of blood transfusion blood components, or tissue	2	3	76	2	1	1	82	2	3	2	158	2
Has HIV infection, risk not specified	25	35	891	19	34	40	960	21	59	37	1,851	20
Receipt of blood transfusion, blood components, or tissue2	2	3	242	5	0	0	143	3	2	1	385	4
Other/risk not reported or identified4	9	13	80	2	8	9	94	2	17	11	174	2
Subtotal	72	100	4,730	100	86	100	4,490	100	158	100	9,220	100
Total	32,585		702,448		11,365		156,550		43,950		859,000
1Includes persons with a diagnosis of AIDS, reported from the beginning of the epidemic through 2002. Cumulative total includes 2 persons of unknown sex.
2AIDS developed in 46 adults/adolescents and 3 children after they received blood that had tested negative for HIV antibodies. AIDS developed in 14 additional adults after they received tissue, organs, or artificial insemination from HIV-infected donors. Four of the 14 received tissue or organs from a donor who was negative for HIV antibody at the time of donation.
3Includes 35 adults/adolescents who were exposed to HIV-infected blood, body fluids, or concentrated virus in health care, laboratory, or household settings, as supported by seroconversion, epidemiologic, and/or laboratory evidence. One person was infected after intentional inoculation with HIV-infected blood. For an additional 288 persons who acquired HIV infection perinatally, AIDS was diagnosed after age 13. These 288 persons are tabulated under the adult/adolescent, not the pediatric, exposure category.
4Includes 5 children who were exposed to HIV-infected blood as supported by seroconversion, epidemiologic, and/or laboratory evidence: 1 child was infected after intentional inoculation with HIV-infected blood and 4 children were exposed to HIV-infected blood in a household setting. Of the 174 children, 22 had sexual contact with an adult with, or at high risk for, HIV infection.
SOURCE: "Table 16. AIDS Cases, by Persons' Age Category, Exposure Category, and Sex, Reported through December 2002—United States," in "Cases of HIV Infection and AIDS in the United States," HIV/AIDS Surveillance Report, vol. 14, October 27, 2003

and women. Table 7.4 shows the number of AIDS cases reported in the United States as of December 2002, by age category, exposure category, and sex. Table 7.5 provides comparable information about cases of HIV infection. Figure 7.2 shows the number of AIDS cases, deaths, and people living with AIDS between 1985 and 2002.

How Is AIDS Spread?

HIV/AIDS is not transmitted through casual contact with an infected person. The CDC has identified several behavioral risk factors that greatly increase the likelihood of a person's chances of being infected. Table 7.6 shows the estimated numbers of those diagnosed with AIDS by year of diagnosis and selected characteristics of patients, including the way in which they contracted the disease.

More than twenty years of research and observation have definitively concluded that the HIV infection can only be transmitted by the following methods:

• By oral, anal, or vaginal sex with an infected person; worldwide, heterosexual sex is the most common mode of transmission

TABLE 7.5
Cases of HIV infection (not AIDS), by persons' age category, exposure category, and sex, from areas with confidental name-based HIV infection reporting, through December 2002

	Males				Females				Totals
	2002		Cumulative through 2002*		2002		Cumulative through 2002*		2002		Cumulative through 2002*
Exposure category	No.	%	No.	%	No.	%	No.	%	No.	%	No.	%
Adult or adolescent
Male-to-male sexual contact	10,991	46	64,331	47	0	0	0	0	10,991	32	64,331	33
Injection drug use	2,149	9	17,312	13	1,253	11	10,123	18	3,402	10	27,436	14
Male-to-male sexual contact and
injection drug use	738	3	7,693	6	0	0	0	0	738	2	7,693	4
Hemophilia/coagulation disorder	27	0	473	0	7	0	47	0	34	0	520	0
Heterosexual contact	1,825	8	10,689	8	3,925	35	24,136	42	5,750	17	34,825	18
Sex with injection drug user	268	1	1,964	1	591	5	5,289	9	859	2	7,253	4
Sex with bisexual male	0	0	0	0	172	2	1,536	3	172	0	1,536	1
Sex with person with hemophilia	4	0	21	0	16	0	164	0	20	0	185	0
Sex with HIV-infected transfusion recipient	17	0	98	0	38	0	167	0	55	0	265	0
Sex with HIV-infected person, risk not specified	1,536	6	8,606	6	3,108	28	16,980	30	4,644	13	25,586	13
Receipt of blood transfusion, blood components, or tissue	56	0	473	0	54	0	490	1	110	0	963	0
Other/risk not reported or identified	7,880	33	37,046	27	5,822	53	22,580	39	13,702	39	59,633	31
Subtotal	23,666	100	138,017	100	11,061	100	57,376	100	34,727	100	195,401	100
Child (<13 yrs)
Hemophilia/coagulation disorder	3	1	105	5	0	0	1	0	3	1	106	2
Mother with, or at risk for, HIV infection	127	60	1,777	82	146	70	1,890	87	273	65	3,667	84
Injection drug use	10	5	502	23	14	7	498	23	24	6	1,000	23
Sex with injection drug user	11	5	188	9	12	6	185	8	23	5	373	9
Sex with bisexual male	3	1	25	1	1	0	17	1	4	1	42	1
Sex with person with hemophilia	0	0	2	0	0	0	7	0	0	0	9	0
Sex with HIV-infected transfusion recipient	0	0	6	0	0	0	5	0	0	0	11	0
Sex with HIV-infected person, risk not specified 35	17	371	17	45	21	458	21	80	19	829	19
Receipt of blood transfusion, blood components, or tissue	0	0	15	1	1	0	16	1	1	0	31	1
Has HIV infection, risk not specified	68	32	668	31	73	35	704	32	141	34	1,372	31
Receipt of blood transfusion, blood components, or tissue	1	0	22	1	1	0	25	1	2	0	47	1
Other/risk not reported or identified	79	38	272	13	63	30	266	12	142	34	538	12
Subtotal ressed to AIDS.	210	100	2,176	100	210	100	2,182	100	420	100	4,358	100
Total	23,876		140,193		11,271		59,558		35,147		199,759
Note: Includes only persons with HIV infection that has not progressed to AIDS.
*Includes persons with a diagnosis of HIV infection (not AIDS), reported from the beginning of the epidemic through December 2002. Cumulative total includes 8 persons of unknown sex.
SOURCE: "Table 17. Cases of HIV Infection (Not AIDS), by Persons' Age Category, Exposure Category, and Sex, Reported through December 2002, from Areas with Confidential Name-Based HIV Infection Reporting," in "Cases of HIV Infection and AIDS in the United States," HIV/AIDS Surveillance Report, vol. 14, October 27, 2003

• By sharing drug needles or syringes with an infected person
• From an infected mother to her baby at the time of birth and possibly through breast milk
• By receiving a transplanted organ or bodily fluids, such as blood transfusions or blood products, from an infected person

Because avoiding these methods of transmission virtually eliminates the possibility of becoming infected with HIV, unlike some other infectious diseases, AIDS is considered almost entirely preventable.

High concentrations of HIV have been found in blood, semen, and cerebrospinal fluid. Concentrations one thousand times less have been found in saliva, tears, vaginal secretions, breast milk, and feces. There have been no reports, however, of HIV transmission from saliva, tears, or human bites. In fact, in 1995 the National Institute of Dental Research in Bethesda, Maryland, reported that a small protein found in human saliva actually blocks the virus from entering the system.

Opportunistic Infections

Once HIV has destroyed the immune system, the body can no longer protect itself against bacterial, fungal, parasitic, or viral agents that take advantage of the compromised condition, causing opportunistic infections (OIs). OIs are illnesses caused by organisms that would not normally harm a healthy person. Because the patient is considered to have AIDS if at least one OI appears, OIs

FIGURE 7.2
TABLE 7.6
Estimated numbers of diagnoses of AIDS, by year of diagnosis and selected characteristics of persons, 1998–2002

are considered "AIDS-defining events." OIs are not the only AIDS-defining events; the diagnosis of malignancies such as Kaposi's sarcoma, Burkitt's lymphoma, invasive cervical cancer, and primary brain lymphoma also are considered AIDS-defining events.

One of the most common opportunistic infections is Pneumocystis carinii pneumonia, a lung infection caused by a fungus. Other infections to which patients with AIDS are susceptible are toxoplasmosis (a contagious disease caused by a one-cell parasite); oral candidiasis (thrush); esophageal or bronchial candidiasis; extrapulmonary cryptococcosis; pulmonary TB; extrapulmonary TB; Mycobacterium avium complex (MAC), a serious bacterial infection that can occur in one part of the body, such as the liver, bone marrow, and spleen, or can spread throughout the body; and cytomegalovirus disease (CMV), a member of the herpes virus group.

Treatment of AIDS

The first drug thought to delay symptoms was zidovudine (earlier known as AZT, later as ZDV), but its effects have been found to be temporary at best. Several other drugs work on the same principle as ZDV, but until the advent of protease inhibitors (PIs), a new class of drugs that became available in the mid-1990s, it seemed that there was no way of stopping HIV. Protease inhibitors appear to keep HIV from reproducing, unlike ZDV and similar drugs, which help keep HIV out of the cell's chromosomes. Even if the PIs are not entirely effective long term in reducing patients' viral "loads," they have improved patients' prospects simply by creating more roadblocks for HIV. Unfortunately, HIV mutates so rapidly that it eventually becomes resistant to most drugs when they are used alone. Even if a cure is never found, new and better drugs used in various combinations may make HIV infection a chronic but manageable disease, much like diabetes.

Treatment recommendations change rapidly in response to the development of new drugs and clinical trials indicating the effectiveness of different combinations of antiretroviral drugs. Researchers are acting quickly to develop new mixtures of the recently approved and older drugs. Because HIV mutates to resist any drug it faces,

TABLE 7.6
Estimated numbers of diagnoses of AIDS, by year of diagnosis and selected characteristics of persons, 1998-2002

	Year of diagnosis
	1998	1999	2000	2001	2002	Cumulative through 20021
Age at diagnosis (yrs)
13	238	183	118	110	92	9,300
13–14	54	58	57	75	76	839
15–124	1,591	1,527	1,625	1,638	1,833	35,460
25–134	12,671	11,342	10,373	10,063	9,688	301,278
35–144	17,670	17,181	17,280	17,057	17,398	347,860
45–154	8,016	8,065	8,581	9,015	9,488	138,386
55–164	2,235	2,218	2,417	2,481	2,773	40,584
≥65 751	739	787	788	789	12,868
Race/ethnicity
White, not Hispanic	13,553	12,626	12,088	11,671	11,929	364,458
Black, not Hispanic	20,672	19,953	20,353	20,594	21,169	347,491
Hispanic	8,460	8,140	8,173	8,279	8,242	163,940
Asian/Pacific Islander	346	380	388	441	478	6,924
American Indian/Alaska Native	157	164	185	188	206	2,875
Exposure category Male adult or adolescent
Male-to-male sexual contact	17,357	16,378	16,076	16,296	16,944	420,790
Injection drug use	8,462	7,965	7,689	7,115	6,945	172,351
Male-to-male sexual contact and injection drug use	2,466	2,275	2,006	2,010	1,898	59,719
Heterosexual contact	4,033	4,136	4,258	4,554	4,937	50,793
Other2	384	365	367	361	365	14,350
Subtotal	32,703	31,119	30,396	30,335	31,089	718,002
Female adult or adolescent
Injection drug use	3,740	3,516	3,533	3,387	3,180	67,917
Heterosexual contact	6,300	6,260	6,911	7,103	7,476	84,835
Other2	243	236	281	292	299	6,519
Subtotal	10,283	10,012	10,725	10,783	10,955	159,271
Child (<13 yrs)
Perinatal	236	181	115	106	90	8,629
Other3	1	2	3	4	2	671
Subtotal	238	183	118	110	92	9,300
Region of residence
Northeast	11,879	11,856	12,400	11,460	10,909	273,248
Midwest	4,061	4,065	4,234	4,305	4,707	87,931
South	18,429	17,184	16,714	17,696	18,546	317,244
West	7,375	6,903	6,646	6,427	6,719	179,212
U.S. dependencies, possessions, and associated nations	1,482	1,305	1,245	1,339	1,256	28,941
Total4	43,225	41,314	41,239	41,227	42,136	886,575
Note: These numbers do not represent actual cases in persons with a diagnosis of AIDS. Rather, these numbers are point estimates of cases diagnosed that have been adjusted for reporting delays and for redistribution of cases in persons initially reported without an identified risk. The estimates have not been adjusted for incomplete reporting.
1Includes persons with a diagnosis of AIDS, from the beginning of the epidemic through 2002.
2Includes hemophilia, blood transfusion, perinatal, and risk not reported or not identified.
3Includes hemophilia, blood transfusion, and risk not reported or not identified.
4Includes persons of unknown or multiple race and of unknown sex. Cumulative total includes 887 persons of unknown or multiple race and 2 persons of unknown sex. Because column totals were calculated independently of the values for the subpopulations, the values in each column may not sum to the column total.
SOURCE: "Table 3. Estimated Numbers of Diagnoses of AIDS, by Year of Diagnosis and Selected Characteristics of Persons, 1998–2002—United States," in "Cases of HIV Infection and AIDS in the United States," HIV/AIDS Surveillance Report, vol. 14, October 27, 2003

including all PIs, researchers have found that varying the combination of drugs prescribed can "fool" the virus before it has time to mutate.

COMPLICATIONS, COSTS, AND SIDE EFFECTS OF TREATMENT.

Patients undergoing therapy with these new drugs or drug combinations must be highly disciplined. For instance, Crixivan must be taken on an empty stomach, every eight hours, not less than two hours before or after a meal, and with large amounts of water to prevent development of kidney stones. Patients also must be careful to never skip doses of Crixivan; otherwise, HIV will quickly grow immune to its effect. (Crixivan has been found to generate cross-resistance, meaning it made patients resistant to other PIs.) Invirase must be taken in large doses. Norvir must be carefully prescribed and administered because it interacts negatively with some antifungals and antibiotics used by patients with AIDS. Because there are a variety of minor and serious risks associated with use of these drugs, patients must be closely monitored by health care practitioners.

The drug regimens are complicated, produce severe side effects in a substantial number of patients, and are costly. The cost of protease inhibitors, such as Viracept and Crixivan, ranges from $4,800 to $8,000 for a year's supply. When combined with ZDV or any of the other commonly used antiretroviral drugs—such as lamivudine (3TC), zalcitabine (ddC), didanosine (ddI), or stavudine (d4T)—the cost is approximately $18,000 per year. Lifetime treatment costs for HIV/AIDS are estimated to be about $155,000. Government programs and private insurers alike are looking for ways to pay for, and in some cases, avoid paying for, these new therapies. As Moises Agosto of the National Minority AIDS Council in Washington, D.C., noted: "We may have all these drugs approved, but if the programs can't afford them, who's going to have access to them?"

HIV and Tuberculosis

TB occurs with increasing frequency among people infected with HIV. In fact, HIV infection has become one of the strongest known risk factors for the progression of TB from infection to disease. A 1996 report from the Conference on Retroviruses and Opportunistic Infections concluded that the decline in CD4+ T-cells is greater in patients with HIV who develop TB than in those who remain free of the disease. In some geographic areas as many as 58 percent of people with TB were HIV-positive.

Of the many diseases associated with HIV infection, TB is one of the few that is transmissible, treatable, and preventable. It is important to note that HIV is a blood-borne infection and cannot be spread through air. A person with HIV who has TB can spread TB nuclei through the air, but they cannot spread HIV this way.