As an alternative approach, we explored using the average length to estimate the source strength of a fully-smoked joint. The 24 marijuana joints used in the present study consisted of 9 different name brands that ranged in length from 59 to 91 mm. The mean length was 79 mm, which was the same as the mean length of the Marlboro cigarettes. Four of the name-brand joints were shorter than the Marlboro cigarette, one was the same length, and four were longer. Like the tobacco cigarettes, each joint had a mouthpiece that acted as a filter. Before and after each joint was smoked in our 24 joint experiments, we measured the length of the portion of the joint that contains the cannabis leaf. Before smoking, the mean length of the cannabis portion was 52.1 mm. After smoking, the mean length of the cannabis portion was reduced to 38.6 mm, indicating that the 3.0-min smoking period used up 52.1–38.6 mm = 13.5 mm of the marijuana-containing portion of the joint. Since this smoking period produced a mean source strength of 23.2 mg , we estimated the average PM2.5 emission per unit smoking length as / = 1.72 mg/mm. Thus, smoking the remaining 38.6 mm was estimated to add the mass emissions of × = 66.4 mg, bringing the estimated mean source strength of the fully smoked joint to 23.2 + 66.4 mg = 89.6 mg. We estimated this large source strength would produce a maximum PM2.5 concentration in the room of 2080 μg/m3 ,pot for cannabis and we estimated the smoking time would be 11.6 min.It also is instructive to compare our tobacco cigarette results with other studies of fully smoked tobacco cigarettes. Chen et al. recruited 2 volunteers to each smoke 5 Chinese tobacco cigarettes in a stainless steel mixing chamber. Their study used mass balance equations like those in the present study to calculate emission rates for each of the 10 fully-smoked cigarettes.

Their observed mean PM2.5 emission rate for the 10 cigarettes was 2.25 mg/min , which was extremely close to our mean emission rate of 2.2 mg/min shown in Table 2. We measured the lengths of the Marlboro tobacco cigarettes used in the present study and found they have a uniform manufactured length of 79 mm, which includes a 24 mm mouthpiece that acts as a filter. As a result, the length of the tobacco-containing portion of the cigarette is 79–24 mm = 55 mm. By measuring the cigarette length before and after each cigarette was smoked, we found the 3-puff protocol used up 31.7 mm of the tobacco-containing portion of the cigarette on average, producing the 6.6 mg average source strength listed in Table 2. Therefore, the Marlboro cigarettes emitted /31.76 mm) = 0.2082 mg/mm on average as they were being smoked, and smoking the remaining 55–31.7 mm = 23.3 mm would add 4.9 mg to the total, bringing the estimated total source strength for a fully smoked tobacco cigarette to 6.6 + 4.9 mg = 11.5 mg. Repace presented a histogram of fine particle mass source strengths of 50 brands of tobacco cigarettes, representing 65.3% of the US market. The average source strength for a fully-smoked cigarette was 13.8 mg , which is close to the 11.5 mg source strength we estimated for a fully smoked Marlboro tobacco cigarette in the present study. Dacunto et al. reported a 19.9 mg source strength for a fully smoked Marlboro cigarette, and Chen et al. reported a mean source strength of 17.3 mg per cigarette for 10 Chinese cigarettes smoked by two volunteer smokers. In the 60 experiments, the mean PM2.5 decay rate for the 9 vaping pen experiments of 0.690 h− 1 was greater than the mean decay rates of the four other sources, which ranged from 0.461 h− 1 to 0.563 h− 1 , and this difference was statistically significant . In comparison, the differences between the decay rates of the joint, bong, glass pipe, and cigarette were not statistically significant. The larger decay rate for the vaping pen appears likely due to the greater volatility of its aerosol. The 24 experiments with 9 different brands of pre-rolled joints produced extremely high PM2.5 concentrations. With just 3 puffs, the maximum PM2.5 concentrations in the room ranged from 143 to 809 μg/ m3 and averaged 540 μg/m3 .

By comparison, the maximum PM2.5 concentrations for the 9 experiments with tobacco cigarettes smoked in the same manner ranged from 22 to 209 μg/m3 and averaged 154 μg/m3 . As a result, the mean secondhand smoke PM2.5 emissions from Marijuana joints was 3.5 times greater than from the tobacco cigarettes. The PM2.5 emissions from the three alternative methods of smoking or vaping marijuana – the bong, glass pipe, and vaping pen – were lower than the emissions of the joint, but all three methods produced greater PM2.5 emissions than the tobacco cigarettes. Zhao et al. conducted a similar set of experiments with an experienced smoker and the same five sources used in the present study. A car parked in a garage to reduce the effect of winds was used as a 6.5 m3 mixing chamber. Like the present study, the marijuana joints had the greatest emission rates, while the tobacco cigarettes had the lowest emission rates. The emission rates of the vaping pen, bong, and glass pipe were in between the marijuana joints and the tobacco cigarettes. Graves et al. measured several thousand different compounds present in mainstream marijuana and mainstream tobacco smoke, as well as Total Particulate Matter mass concentrations. They collected the TPM on 47 mm quartz filters that were weighed on a laboratory microbalance. They report that the average TPM concentration in marijuana mainstream smoke was 3.4 times greater than the TPM concentration in mainstream tobacco smoke. Their 95% confidence interval around this ratio was ±0.6, and thus our ratio of 3.5 for the marijuana joint emission rate relative to the tobacco cigarette emission rate was within their 95% confidence interval. However, their result was for mainstream smoke, while our result was for secondhand smoke, which is a combination of mainstream and side stream smoke. Moir et al. reported the mainstream TPM mass concentrations in marijuana smoke was about the same as in tobacco smoke. They also measured the mass concentrations of 30 PAH compounds in both marijuana and tobacco smoke. Their study indicated that 89.8% of the PAHs in secondhand marijuana smoke were from side stream emissions while 10.2% were from mainstream emissions. McClure et al. reported that the volume of the puffs from an adult smoker decreases steadily over the course of smoking a cigarette.

Wu et al. studied 15 habitual marijuana smokers and reported the puff volume was smaller for the second half than for the first half of marijuana cigarettes, while Tashkin et al. reported mainstream CO, tar, and THC emissions were greater for the second half than for the first half of a marijuana cigarette. For estimating secondhand smoke emissions from a fully-smoked tobacco or marijuana cigarette, we feel our assumed linear relationship between secondhand smoke emissions and length smoked is reasonable and would be a good topic for future research. Since the marijuana joint has a long history of use and is one of the most popular methods of consuming cannabis, we chose the largest sample size, n = 24 experiments, for the pre-rolled joint. The bong, glass pipe, vaping pen, and cigarette all had smaller sample sizes of n = 9 experiments. Except for one case, the differences in the PM2.5 emission rates between these four common methods of consuming marijuana or tobacco based on 9 experiments did not reach statistical significance at the p < 0.05 level. The 24 marijuana joints used in the present study were obtained from four state-licensed stores in three California towns, and the joints included 9 different name brands that are popular in California. Only two different kinds of marijuana buds were used in the bong and glass pipe experiments, however, and the results should show greater variation if more types of cannabis buds were included and if sample sizes were larger. The Absolute Xtracts vaping pen used in the present study is battery-powered and uses an electronic microprocessor that controls the temperature of the vaping fluid. This vaping pen has several settings that a user can select by pressing a button on the side of the pen. In our vaping pen experiments, we chose the “pre-heat” mode recommended in the ABX instructions, and we selected the highest of three power levels. This approach pre-heats the vaping liquid for 15 s, followed by the 3-puff protocol that started within 1-1/2 min after preheating ended. A user might choose different settings of this vaping pen that could result in greater or lesser emissions. Using an identical ABX vaping pen, Wallace et al. reported that two different vaping protocols produced two different temperatures, resulting in about 3 times greater source strength for the high-heat protocol than for the low-heat protocol. In the present study, the 9 pot for growing marijuana vaping experiments were limited to two different commercial vaping cartridges. Many other vaping cartridges are available with different levels of THC and CBD that could be compared in a future study with a larger sample size. To compare different source types with each other, the 60 experiments in this study used the same smoker, while future studies may choose to explore differences among smokers. Hepatitis C virus co-infection is common amongst HIV-infected persons, affecting an estimated 4 to 5 million persons worldwide, and is associated with increased morbidity and mortality. Whereas the primary route of HCV transmission remains injection drug use , over recent years there has been increasing evidence of sexual transmission among HIV-infected men who have sex with men , likely driven by mucosal risk factors, including unprotected and traumatic sexual practices in the context of multiple partners, non-injection drug use, and sexually transmitted infections. Prevalence estimates for HCV co-infection in HIV-infected MSM have ranged from 6 to 15.7 %, with limited geographic characterization. The prevalence of HCV co-infection in HIV-infected MSM in Los Angeles County in the U.S. has not been defined, despite LAC being the second largest epicenter for AIDS cases nationally, with high rates of non-injection drug use and high-risk sexual practices. Our aims were to characterize the prevalence of and risk factors for HCV co-infection and patterns of HIV and HCV co-transmission and drug resistance mutations in a cohort of newly HIV-infected or HIV-diagnosed Los Angeles MSM.

Prevalence of HCV co-infection was low and there was no evidence of HIV-HCV co-transmission in this cohort of young, predominantly minority, newly HIV-diagnosed MSM. The majority of subjects had recent HIV infection and notable behavioral and clinical risk factors for sexual HCV transmission, including high-risk sexual practices, sexually transmitted infections, and non-injection substance use, with low rates of injection drug use. The lower prevalence of HCV compared with other HIV-infected MSM cohorts may reflect the younger age of the cohort with fewer cumulative exposures to HCV, lower rates of IDU, relatively greater immune preservation with earlier HIV infection, and identification of HCV by HCV RNA instead of by serology. In our study, by measuring HCV RNA, we measured prevalence of active HCV replication and not exposure or infection with possible clearance, as would be measured by serology. Assessment by both serology and HCV RNA would provide broader characterization of HCV exposure in the cohort, but due to limited sample volume, we could not perform testing for both and elected for HCV RNA testing alone as a measure of active HCV infection and risk for HCV transmission. Demographically, our cohort differed from others in its geographic and racial/ethnic composition, wherein our cohort was predominantly of minority race and half was Hispanic, as compared to most other reported cohorts that were predominantly White. The epidemiology of HCV co-infection in HIV-infected Hispanic MSM has not been well described. As described by Kunikholm et al., utilizing National Health and Nutrition Examination Survey and Hispanic Community Health Study/Study of Latinos data, HCV prevalence appears to differ by Hispanic/Latino background and the prevalence of HCV in the West Coast Hispanic population may be lower than in others [13]. While there were too few subjects with HCV infection in the cohort to explore associations between potential behavioral risk factors and HCV infection, the subjects that did have HCV co-infection all reported methamphetamine and other non-injection drug use, as well as high-risk sexual practices, consistent with risk factors identified in larger cohorts.