Birth control resident survival guide
Birth control Resident Survival Guide Microchapters |
---|
Overview |
Birth Control Options |
Female Options |
Male Options |
Indications |
Contraindications |
Emergency Contraception |
Side Effects |
Eligibility Criteria |
Dos |
Don'ts |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Huda A. Karman, M.D.
Synonyms and keywords: Contraception options, Birth control options, Planned parenthood, Birth prevention, Family planning, Conception prevention
Overview
Contraception or birth control is mainly used for the prevention of unwanted pregnancy intentionally by using one of many different methods including devices, sexual practices, chemicals, drugs or surgical procedures. Contraception methods can also be used for other purposes such as prevention of sexual transmitted infection, treatment of different conditions such as acne, polycystic ovary syndrome, endometriosis, amenorrhea, dysmenorrhea, premenstrual syndrome, primary ovarian insufficiency, and heavy menstrual periods. Health care providers should consider the important elements when choosing the most appropriate contraceptive method for women, men, or couples such as safety, effectiveness, availability (including accessibility and affordability), and acceptability. CDC has created recommendations and categories for the use of birth control based on the element of safety.
Birth Control Options
Female birth control options
Long-acting reversible contraception (LARC): is 99% effective, has a high rate of satisfaction, long-term use, quick return to fertility when discontinued and includes the following:[1]
- Intrauterine device (IUDs) (> 99% effective)[2]
- Copper IUD: Effective for up to 10 years, used for patients with light menstrual periods, patients who desire long-term contraception without using hormonal contraception
- Progestin-releasing IUD: Effective for up to 5 years, used for patients with heavy menstrual bleeding and dysmenorrhea
- Subdermal implant (> 99% effective): Effective for up to 3 years[3]
Injectable contraception[4]
- Depot-Medroxyprogesterone: (94% effective), IM injection is given every 3 months
Combined hormonal contraceptives[5]
- Oral contraceptive (estrogen/progestin pills) (OCPs) (91% effective)
- Contraceptive patch (91% effective)
- Vaginal Ring (91% effective)
Barrier and chemical methods[6][7]
- Female Condom
- Diaphragm
- Cervical Cap
- Sponge
- Spermicide (80% failure rate if used alone). Should be used with cervical cap or diaphragm, may damage the genital epithelium and increase risk of acquiring SDIs[8]
Traditional options/Natural contraception[9]
- Fertility awareness[10]
- Lactational Amenorrhea Method (LAM) (Breastfeeding can help with child spacing)[11]
- Abstinence or withdrawal
- Rhythm Method
Surgical options
- Permanent Sterilization (Tubectomy/tubal ligation)[12][13]
Male birth control options
Male contraception includes the following:[15]
- Condoms (80% effective), the only type of contraception that prevent sexually transmitted infections[16]
Male Sterilization
Coitus Interruptus or Withdrawal (75% effective)[19]
- Testosterone in combination with other hormones under research and development[21]
- Testosterone enanthate: intramuscular short-acting testosterone formulations suppresses sperm concentration to very low levels[22]
- Long-acting intramuscular testosterone undecanoate[23]
Hormonal contraceptive injectable regimes using testosterone combined with other molecules
- Testosterone plus progestin[24]
- Testosterone plus Gonadotropin Releasing Hormone (GnRH) antagonists[25]
- Hormonal contraceptive transdermal regimes using testosterone and Nestorone: gel-gel combination[26][27]
- Oral formulations: the male pill [28]
Indications
- Contraceptive use: Prevention of unwanted pregnancy
- Non-contraceptive use: Treatment of different conditions such as:[29]
- Acne
- Amenorrhea
- Dysmenorrhea
- Endometriosis
- Heavy menstrual periods
- Premenstrual syndrome (PMS)
- Primary ovarian insufficiency (POI)
- Polycystic ovary syndrome (PCOS): OCPs are used for menstrual regulation
Contraindications
Combined hormonal contraceptives
Absolute contraindications[5]
- Pregnancy
- Less than 6 wks postpartum
- Smoking (age ≥ 35, and ≥15 cigarettes per day)
- Hypertension (systolic ≥ 160mmHg or diastolic ≥100mmHg)
- Venous thromboembolism (VTE) (current of past history)
- Prior history of throboembolic event or stroke
- Thrombophilia (factor V Leiden, APLS)
- Ischemic heart disease
- Cerebrovascular accident history
- Complicated valvular heart disease (pulmonary hypertension, atrial fibrillation, history of subacute bacterial endocarditis)
- Migraine headache with aura or focal neurological symptoms
- Breast cancer (Active)
- History of an estrogen-dependent tumor
- Diabetes with retinopathy/nephropathy/neuropathy
- Severe cirrhosis (active or severe decompensated liver disease) (impair steroid metabolism)
- Liver tumor (adenoma or hepatoma)
- Hypertriglyceridemia
Relative contraindication[5]
- Age ≥ 35 and smoking < 15 cigarettes per day
- Adequately controlled mild hypertension
- Hypertension (systolic 140 - 159mmHg or diastolic 90 - 99mmHg)
- Migraine headache over the age of 35
- Currently symptomatic gallbladder disease
- Mild cirrhosis
- History of combined OCP-related cholestasis
- Medications that interfere with OCPs: Lamotrigine, Rifampin
- Inherited thrombophilia carrier and family member with thrombophilia plus thromboembolism
IUDs
- Uterine anomalies or severe distortion
- Active pelvic infection
- Wilson disease
- Complicated organ transplant failure
Subdermal implant
- Progesterone receptor-positive breast cancer
Emergency Contraception
Contracetion option | Hours after intercourse | Efficacy |
---|---|---|
Copper containing IUD | 0 to 120 hour/5 days | >99% |
Ulipristal | 0 to 120 hour/5 days | 98-99% |
Levonorgestril | 0 to 72 hour/3 days | 59-94% |
Oral contraceptive pills | 0 to 72 hour/3 days | 47-89% |
Side Effects
Contraceptive method | Side effects |
---|---|
Combined hormonal contraceptives
(OCPs, patch, ring) |
Breakthrough menstrual bleeding
Breast Tenderness Nausea Weight gain Rare side effects: Cardiovascular events (heavy smoker, over age 35 years)
|
Subdermal implant | Unscheduled bleeding,
Weight gain Headache Ovulation and fertility occur within one month after removal |
DMPA | Amenorrheah
Initial irregular bleeding Reversible bone loss, delayed return to fertility, +/- weight gain |
Progestin IUD | Amenorrhea
Irregular bleeding |
Copper IUD | Heavy menses
Menestrual and intermenestrual pain Dysmenorrhea |
Spermicide | May damage the genital epithelium and increase risk of acquiring SDIs |
U.S. Medical Eligibility Criteria for Contraceptive Use (MEC), 2016
Abbreviations: BMI: body mass index; CHC: combined hormonal contraceptive; COC: combined oral contraceptive; Cu-IUD: copper-containing intrauterine device; ECP: emergency contraceptive pill; IUD: intrauterine device; LNG: levonorgestrel; POC: progestin-only contraceptive; STD: sexually transmitted disease; UPA: ulipristal acetate
Women, men, or couples should consider the following elements when choosing the most appropriate contraceptive method:
- Safety
- Effectiveness
- Availability (including accessibility and affordability)
- Acceptability
- Categories of medical eligibility criteria for contraceptive use
Category | Characteristics |
---|---|
1 | A condition for which there is no restriction for the use of the contraceptive method |
2 | A condition for which the advantages of using the method generally outweigh the theoretical or proven risks |
3 | A condition for which the theoretical or proven risks usually outweigh the advantages of using the method |
4 | A condition that represents an unacceptable health risk if the contraceptive method is used |
The following table focuses on the safety of the use of the contraceptive method for a person with a particular characteristic based on CDC guidelines and recommendations:
Condition | Category | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | ||||||||
Breastfeeding
<21 days postpartum |
Implants
DMPA POP |
CHCs | |||||||||
21 to <30 days postpartum
With other risk factors for VTE |
Implants
DMPA POP |
CHCs | |||||||||
21 to <30 days postpartum
Without other risk factors for VTE |
Implants
DMPA POP |
CHCs | |||||||||
30–42 days postpartum
With other risk factors for VTE |
Implants
DMPA POP |
CHCs | |||||||||
30–42 days postpartum
Without other risk factors for VTE |
Implants
DMPA POP |
CHCs | |||||||||
>42 days postpartum | Implants
DMPA POP |
CHCs | |||||||||
Postpartum (non-breastfeeding women)
<21 days postpartum |
Implants
DMPA POP |
CHCs | |||||||||
Postpartum (non-breastfeeding women)
21–42 days postpartum With other risk factors for VTE |
Implants
DMPA POP |
CHCs | |||||||||
Postpartum (non-breastfeeding women)
21–42 days postpartum Without other risk factors for VTE |
Implants
DMPA POP |
CHCs | |||||||||
Postpartum (non-breastfeeding women)
>42 days postpartum |
CHCs
Implants DMPA POP |
||||||||||
Postpartum (including cesarean delivery)
<10 minutes after delivery of the placenta Breastfeeding |
Cu-IUD | LNG-IUD | |||||||||
Postpartum (including cesarean delivery)
a. <10 minutes after delivery of the placenta Non-breastfeeding |
Cu-IUD
LNG-IUD |
||||||||||
10 minutes after delivery of the placenta to <4 weeks
(breastfeeding or non-breastfeeding) |
Cu-IUD
LNG-IUD |
||||||||||
≥4 weeks (breastfeeding or non-breastfeeding) | Cu-IUD
LNG-IUD |
||||||||||
Postpartum sepsis | Cu-IUD
LNG-IUD | ||||||||||
Multiple risk factors
for atherosclerotic cardiovascular disease |
Cu-IUD | LNG-IUD
Implants POP |
CHCs
DMPA
|
CHCs | |||||||
Superficial venous disorders
Varicose veins |
Cu-IUD
LNG-IUD Implants DMPA POP CHCs |
CHCs | |||||||||
Superficial venous disorders
Superficial venous thrombosis (acute or history) |
Cu-IUD
LNG-IUD Implants DMPA POP |
CHCs | |||||||||
Headaches
Non-migraine (mild or severe) |
Cu-IUD
LNG-IUD Implants DMPA POP CHCs |
||||||||||
Migraine
Without aura (includes menstrual migraine)
|
Cu-IUD
LNG-IUD Implants DMPA POP
|
CHCs | |||||||||
Migraine with aura | Cu-IUD
LNG-IUD Implants DMPA POP |
CHCs | |||||||||
Multiple sclerosis
With prolonged immobility |
Cu-IUD
LNG-IUD Implants POP |
DMPA | CHCs | ||||||||
Multiple sclerosis
Without prolonged immobility |
Cu-IUD
LNG-IUD Implants POP |
DMPA | |||||||||
Suspected Gestational trophoblastic disease
(immediate post-evacuation) Uterine size first trimester |
Cu-IUD
LNG-IUD Implants DMPA POP CHCs |
||||||||||
Suspected Gestational trophoblastic disease
(immediate post-evacuation) Uterine size second trimester |
Implants
DMPA POP CHCs |
Cu-IUD
LNG-IUD |
|||||||||
Confirmed gestational trophoblastic disease
(after the initial evacuation and during monitoring) Undetectable/nonpregnant β-hCG levels
|
Cu-IUD
LNG-IUD Implants DMPA POP CHCs |
||||||||||
Decreasing β-hCG levels
|
Cu-IUD (continuation)
LNG-IUD (continuation) Implants DMPA POP CHCs |
Cu-IUD (initiation)
LNG-IUD (initiation) |
|||||||||
Persistently elevated β-hCG levels or malignant disease,
with no evidence or suspicion of intrauterine disease
|
Cu-IUD (continuation)
LNG-IUD (continuation) Implants DMPA POP CHCs |
Cu-IUD (initiation)
LNG-IUD (initiation) |
|||||||||
Persistently elevated β-hCG levels or malignant disease,
with evidence or suspicion of intrauterine disease |
Implants
DMPA POP CHCs |
Cu-IUD (continuation)
LNG-IUD (continuation) |
Cu-IUD (initiation)
LNG-IUD (initiation) | ||||||||
Sexually transmitted diseases
or chlamydial infection or gonococcal infection
|
Implants
DMPA POP CHCs |
Cu-IUD (continuation)
LNG-IUD (continuation) |
Cu-IUD (initiation)
LNG-IUD (initiation) | ||||||||
Vaginitis
(including Trichomonas vaginalis and bacterial vaginosis) |
Implants
DMPA POP CHCs |
Cu-IUD (initiation)
LNG-IUD (initiation)
LNG-IUD (continuation) |
|||||||||
High risk for HIV | Implants
DMPA POP CHCs |
Cu-IUD (initiation)
LNG-IUD (initiation)
LNG-IUD (continuation) |
|||||||||
HIV infection | Implants
DMPA POP CHCs |
||||||||||
Clinically well receiving ARV therapy |
Cu-IUD (initiation)
LNG-IUD (initiation)
LNG-IUD (continuation) |
||||||||||
HIV infection
Not clinically well or not receiving ARV therapy |
Cu-IUD (continuation)
LNG-IUD (continuation) |
Cu-IUD (initiation)
LNG-IUD (initiation) |
|||||||||
Cystic fibrosis | Cu-IUD
LNG-IUD Implants POP CHCs |
DMPA | |||||||||
Antiretroviral therapy
Nucleoside reverse transcriptase inhibitors (NRTIs) |
Cu-IUD (initiation)
Cu-IUD (continuation) LNG-IUD (initiation) |
Cu-IUD (initiation)
LNG-IUD (initiation) LNG-IUD (continuation) |
|||||||||
Nonnucleoside reverse transcriptase inhibitors (NNRTIs) | Cu-IUD (initiation)
Cu-IUD (continuation) LNG-IUD (initiation) DMPA |
Cu-IUD (initiation)
LNG-IUD (initiation) LNG-IUD (continuation) Implants POP CHCs |
|||||||||
Ritonavir-boosted protease inhibitors | Cu-IUD (initiation)
Cu-IUD (continuation) LNG-IUD (initiation) DMPA |
Cu-IUD (initiation)
LNG-IUD (initiation) LNG-IUD (continuation) Implants POP CHCs
|
|||||||||
Protease inhibitors without ritonavir | Cu-IUD (initiation)
Cu-IUD (continuation) LNG-IUD (initiation) LNG-IUD (continuation) DMPA Implants POP CHCs |
Cu-IUD (initiation)
LNG-IUD (initiation) |
|||||||||
CCR5 co-receptor antagonists | Cu-IUD (initiation)
Cu-IUD (continuation) LNG-IUD (initiation) LNG-IUD (continuation) DMPA Implants POP CHCs |
Cu-IUD (initiation)
LNG-IUD (initiation) |
|||||||||
HIV integrase strand transfer inhibitors | Cu-IUD (initiation)
Cu-IUD (continuation) LNG-IUD (initiation) LNG-IUD (continuation) DMPA Implants POP CHCs |
Cu-IUD (initiation)
LNG-IUD (initiation) |
|||||||||
Fusion inhibitors | Cu-IUD (initiation)
Cu-IUD (continuation) LNG-IUD (initiation) LNG-IUD (continuation) DMPA Implants POP CHCs |
Cu-IUD (initiation)
LNG-IUD (initiation) |
|||||||||
Psychotropic medications a. SSRIs | Cu-IUD
LNG-IUD DMPA Implants POP CHCs |
||||||||||
St. John’s wort | Cu-IUD
LNG-IUD DMPA |
Implants
POP CHCs |
|||||||||
Dos
- Increase the levothyroxine dose in patients with hypothyroidism who started taking OCPs. Oral contraceptives (estrogen) alter the transport and tissue delivery of thyroid hormone by increasing the synthesis of throxine-binding globulin which can lead to a relative hypothyroid state in patients with hypothyroidism.
- Consider increasing the dose of warfarin when the patient uses OCPs
- Give two forms of contraceptives and take monthly pregnancy tests for sexually active women who use Isotretinoin for acne
- Give non-oral form of contraception (IUD, implant) for one year to patients who underwent bariatric surgery to achieve weight loss goals and stabilize nutritional status
- You can use IUD in a nulliparous female who has no contraindications
Don'ts
- Don't give CHC to a patient of age ≥ 35 who smokes ≥15 cigarettes per day
- Don't give CHC for a patient with history of Migraine headache with aura or focal neurological symptoms
References
- ↑ Stoddard A, McNicholas C, Peipert JF (2011). "Efficacy and safety of long-acting reversible contraception". Drugs. 71 (8): 969–80. doi:10.2165/11591290-000000000-00000. PMC 3662967. PMID 21668037.
- ↑ Blumenthal PD, Voedisch A, Gemzell-Danielsson K (2011). "Strategies to prevent unintended pregnancy: increasing use of long-acting reversible contraception". Hum Reprod Update. 17 (1): 121–37. doi:10.1093/humupd/dmq026. PMID 20634208.
- ↑ Jacobstein R, Stanley H (2013). "Contraceptive implants: providing better choice to meet growing family planning demand". Glob Health Sci Pract. 1 (1): 11–7. doi:10.9745/GHSP-D-12-00003. PMC 4168562. PMID 25276512.
- ↑ Kaunitz AM (1992). "Injectable contraception: the USA perspective". IPPF Med Bull. 26 (6): 1–3. PMID 12346920.
- ↑ 5.0 5.1 5.2 Rager KM, Omar HA (2005). "Hormonal contraception: noncontraceptive benefits and medical contraindications". Adolesc Med Clin. 16 (3): 539–51. doi:10.1016/j.admecli.2005.05.003. PMID 16183538.
- ↑ Gilliam ML, Derman RJ (2000). "Barrier methods of contraception". Obstet Gynecol Clin North Am. 27 (4): 841–58. doi:10.1016/s0889-8545(05)70174-1. PMID 11091990.
- ↑ Craig S, Hepburn S (1982). "The effectiveness of barrier methods of contraception with and without spermicide". Contraception. 26 (4): 347–59. doi:10.1016/0010-7824(82)90102-0. PMID 6759027.
- ↑ Harwood B, Meyn LA, Ballagh SA, Raymond EG, Archer DF, Creinin MD (2008). "Cervicovaginal colposcopic lesions associated with 5 nonoxynol-9 vaginal spermicide formulations". Am J Obstet Gynecol. 198 (1): 32.e1–7. doi:10.1016/j.ajog.2007.05.020. PMC 4332520. PMID 18166301.
- ↑ Ajayi AI, Adeniyi OV, Akpan W (2018). "Use of traditional and modern contraceptives among childbearing women: findings from a mixed methods study in two southwestern Nigerian states". BMC Public Health. 18 (1): 604. doi:10.1186/s12889-018-5522-6. PMC 5941455. PMID 29739372.
- ↑ Peragallo Urrutia R, Polis CB, Jensen ET, Greene ME, Kennedy E, Stanford JB (2018). "Effectiveness of Fertility Awareness-Based Methods for Pregnancy Prevention: A Systematic Review". Obstet Gynecol. 132 (3): 591–604. doi:10.1097/AOG.0000000000002784. PMID 30095777.
- ↑ Van der Wijden C, Manion C (2015). "Lactational amenorrhoea method for family planning". Cochrane Database Syst Rev (10): CD001329. doi:10.1002/14651858.CD001329.pub2. PMC 6823189 Check
|pmc=
value (help). PMID 26457821. - ↑ Patil E, Jensen JT (2015). "Update on permanent contraception options for women". Curr Opin Obstet Gynecol. 27 (6): 465–70. doi:10.1097/GCO.0000000000000213. PMC 4678034. PMID 26406934.
- ↑ Bartz D, Greenberg JA (2008). "Sterilization in the United States". Rev Obstet Gynecol. 1 (1): 23–32. PMC 2492586. PMID 18701927.
- ↑ Schiavon R, Jiménez-Villanueva CH, Ellertson C, Langer A (2000). "[Emergency contraception: a simple, safe, effective and economical method for preventing undesired pregnancy]". Rev Invest Clin. 52 (2): 168–76. PMID 10846441.
- ↑ Mathew V, Bantwal G (2012). "Male contraception". Indian J Endocrinol Metab. 16 (6): 910–7. doi:10.4103/2230-8210.102991. PMC 3510960. PMID 23226635.
- ↑ Gallo MF, Grimes DA, Schulz KF (2003). "Non-latex versus latex male condoms for contraception". Cochrane Database Syst Rev (2): CD003550. doi:10.1002/14651858.CD003550. PMID 12804475.
- ↑ Kumar V, Kaza RM, Singh I, Singhal S, Kumaran V (1999). "An evaluation of the no-scalpel vasectomy technique". BJU Int. 83 (3): 283–4. doi:10.1046/j.1464-410x.1999.00934.x. PMID 10233495.
- ↑ Dassow P, Bennett JM (2006). "Vasectomy: an update". Am Fam Physician. 74 (12): 2069–74. PMID 17186713.
- ↑ Horner JR, Salazar LF, Romer D, Vanable PA, DiClemente R, Carey MP; et al. (2009). "Withdrawal (coitus interruptus) as a sexual risk reduction strategy: perspectives from African-American adolescents". Arch Sex Behav. 38 (5): 779–87. doi:10.1007/s10508-007-9304-y. PMC 4218729. PMID 18293076.
- ↑ Gava G, Meriggiola MC (2019). "Update on male hormonal contraception". Ther Adv Endocrinol Metab. 10: 2042018819834846. doi:10.1177/2042018819834846. PMC 6419257. PMID 30899448.
- ↑ Cheng CY, Mruk DD (2010). "New frontiers in nonhormonal male contraception". Contraception. 82 (5): 476–82. doi:10.1016/j.contraception.2010.03.017. PMC 4381878. PMID 20933122.
- ↑ Steinberger E, Smith KD (1977). "Testosterone enanthate a possible reversible male contraceptive". Contraception. 16 (3): 261–8. doi:10.1016/0010-7824(77)90025-7. PMID 913115.
- ↑ Gu YQ, Wang XH, Xu D, Peng L, Cheng LF, Huang MK; et al. (2003). "A multicenter contraceptive efficacy study of injectable testosterone undecanoate in healthy Chinese men". J Clin Endocrinol Metab. 88 (2): 562–8. doi:10.1210/jc.2002-020447. PMID 12574181.
- ↑ Meriggiola MC, Farley TM, Mbizvo MT (2003). "A review of androgen-progestin regimens for male contraception". J Androl. 24 (4): 466–83. doi:10.1002/j.1939-4640.2003.tb02695.x. PMID 12826683.
- ↑ Pavlou SN, Brewer K, Farley MG, Lindner J, Bastias MC, Rogers BJ; et al. (1991). "Combined administration of a gonadotropin-releasing hormone antagonist and testosterone in men induces reversible azoospermia without loss of libido". J Clin Endocrinol Metab. 73 (6): 1360–9. doi:10.1210/jcem-73-6-1360. PMID 1955518.
- ↑ Sitruk-Ware R, Nath A (2010). "The use of newer progestins for contraception". Contraception. 82 (5): 410–7. doi:10.1016/j.contraception.2010.04.004. PMID 20933114.
- ↑ Ilani N, Roth MY, Amory JK, Swerdloff RS, Dart C, Page ST; et al. (2012). "A new combination of testosterone and nestorone transdermal gels for male hormonal contraception". J Clin Endocrinol Metab. 97 (10): 3476–86. doi:10.1210/jc.2012-1384. PMC 3462927. PMID 22791756.
- ↑ Meriggiola MC, Bremner WJ, Costantino A, Pavani A, Capelli M, Flamigni C (1997). "An oral regimen of cyproterone acetate and testosterone undecanoate for spermatogenic suppression in men". Fertil Steril. 68 (5): 844–50. doi:10.1016/s0015-0282(97)00363-4. PMID 9389813.
- ↑ Fraser IS (2010). "Non-contraceptive health benefits of intrauterine hormonal systems". Contraception. 82 (5): 396–403. doi:10.1016/j.contraception.2010.05.005. PMID 20933112.
- ↑ "Emergency contraception". Paediatr Child Health. 8 (3): 181–92. 2003. doi:10.1093/pch/8.3.181. PMC 2792670. PMID 20020019.
- ↑ Hubacher D, Chen PL, Park S (2009). "Side effects from the copper IUD: do they decrease over time?". Contraception. 79 (5): 356–62. doi:10.1016/j.contraception.2008.11.012. PMC 2702765. PMID 19341847.
- ↑ Sanders JN, Adkins DE, Kaur S, Storck K, Gawron LM, Turok DK (2018). "Bleeding, cramping, and satisfaction among new copper IUD users: A prospective study". PLoS One. 13 (11): e0199724. doi:10.1371/journal.pone.0199724. PMC 6221252. PMID 30403671.
- ↑ "www.cdc.gov" (PDF).